|**Fair Values of Assets and Liabilities - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands**            | Jun. 30, 2022                                                                         | Dec. 31, 2021                                                                        
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                      |                                                                                       |                                                                                      
|Other investments                                                                                                                                                     | $ 13,665                                                                              |                                                                                      
|Loans Held for Sale                                                                                                                                                   | 12,876                                                                                |                                                                                      
|Other Assets                                                                                                                                                          | 42,597                                                                                | [1]                                                                                  
|Total Assets                                                                                                                                                          | 932,760                                                                               |                                                                                      
|Other Liabilities                                                                                                                                                     | 55,435                                                                                | [1]                                                                                  
|Total Liabilities                                                                                                                                                     | 55,435                                                                                |                                                                                      
|Investments, Fair Value Disclosure                                                                                                                                    | 863,622                                                                               |                                                                                      
|Limited Partnership Investment [Member]                                                                                                                               |                                                                                       |                                                                                      
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                      |                                                                                       |                                                                                      
|Total Assets                                                                                                                                                          | 16,613                                                                                |                                                                                      
|US Government Agencies Residential Mortgage-backed Securities [Member]                                                                                                |                                                                                       |                                                                                      
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                      |                                                                                       |                                                                                      
|Investments, Fair Value Disclosure                                                                                                                                    | 4,694                                                                                 |                                                                                      
|US Government Agency Debt Securities Commercial [Member]                                                                                                              |                                                                                       |                                                                                      
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                      |                                                                                       |                                                                                      
|Investments, Fair Value Disclosure                                                                                                                                    | 308,870                                                                               |                                                                                      
|Residential Mortgage Backed Securities [Member]                                                                                                                       |                                                                                       |                                                                                      
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                      |                                                                                       |                                                                                      
|Investments, Fair Value Disclosure                                                                                                                                    | 509,530                                                                               |                                                                                      
|Obligations of U.S. Government-Sponsored Enterprises - Other Government-Sponsored Enterprises [Member]                                                                |                                                                                       |                                                                                      
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                      |                                                                                       |                                                                                      
|Investments, Fair Value Disclosure                                                                                                                                    | 919                                                                                   |                                                                                      
|Obligations of States and Political Subdivisions [Member]                                                                                                             |                                                                                       |                                                                                      
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                      |                                                                                       |                                                                                      
|Investments, Fair Value Disclosure                                                                                                                                    | 8,591                                                                                 |                                                                                      
|Corporate Debt Securities [Member]                                                                                                                                    |                                                                                       |                                                                                      
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                      |                                                                                       |                                                                                      
|Investments, Fair Value Disclosure                                                                                                                                    | 31,018                                                                                |                                                                                      
|Level 1 [Member]                                                                                                                                                      |                                                                                       |                                                                                      
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                      |                                                                                       |                                                                                      
|Other investments                                                                                                                                                     | 0                                                                                     |                                                                                      
|Loans Held for Sale                                                                                                                                                   | 0                                                                                     |                                                                                      
|Other Assets                                                                                                                                                          | 0                                                                                     | [1]                                                                                  
|Total Assets                                                                                                                                                          | 0                                                                                     |                                                                                      
|Other Liabilities                                                                                                                                                     | 0                                                                                     | [1]                                                                                  
|Total Liabilities                                                                                                                                                     | 0                                                                                     |                                                                                      
|Investments, Fair Value Disclosure                                                                                                                                    | 0                                                                                     |                                                                                      
|Level 1 [Member] | US Government Agencies Residential Mortgage-backed Securities [Member]                                                                             |                                                                                       |                                                                                      
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                      |                                                                                       |                                                                                      
|Investments, Fair Value Disclosure                                                                                                                                    | 0                                                                                     |                                                                                      
|Level 1 [Member] | US Government Agency Debt Securities Commercial [Member]                                                                                           |                                                                                       |                                                                                      
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                      |                                                                                       |                                                                                      
|Investments, Fair Value Disclosure                                                                                                                                    | 0                                                                                     |                                                                                      
|Level 1 [Member] | Residential Mortgage Backed Securities [Member]                                                                                                    |                                                                                       |                                                                                      
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                      |                                                                                       |                                                                                      
|Investments, Fair Value Disclosure                                                                                                                                    | 0                                                                                     |                                                                                      
|Level 1 [Member] | Obligations of U.S. Government-Sponsored Enterprises - Other Government-Sponsored Enterprises [Member]                                             |                                                                                       |                                                                                      
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                      |                                                                                       |                                                                                      
|Investments, Fair Value Disclosure                                                                                                                                    | 0                                                                                     |                                                                                      
|Level 1 [Member] | Obligations of States and Political Subdivisions [Member]                                                                                          |                                                                                       |                                                                                      
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                      |                                                                                       |                                                                                      
|Investments, Fair Value Disclosure                                                                                                                                    | 0                                                                                     |                                                                                      
|Level 1 [Member] | Corporate Debt Securities [Member]                                                                                                                 |                                                                                       |                                                                                      
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                      |                                                                                       |                                                                                      
|Investments, Fair Value Disclosure                                                                                                                                    | 0                                                                                     |                                                                                      
|Level 2 [Member]                                                                                                                                                      |                                                                                       |                                                                                      
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                      |                                                                                       |                                                                                      
|Other investments                                                                                                                                                     | 12,495                                                                                |                                                                                      
|Loans Held for Sale                                                                                                                                                   | 12,876                                                                                |                                                                                      
|Other Assets                                                                                                                                                          | 25,984                                                                                | [1]                                                                                  
|Total Assets                                                                                                                                                          | 914,977                                                                               |                                                                                      
|Other Liabilities                                                                                                                                                     | 55,435                                                                                | [1]                                                                                  
|Total Liabilities                                                                                                                                                     | 55,435                                                                                |                                                                                      
|Investments, Fair Value Disclosure                                                                                                                                    | 863,622                                                                               |                                                                                      
|Level 2 [Member] | US Government Agencies Residential Mortgage-backed Securities [Member]                                                                             |                                                                                       |                                                                                      
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                      |                                                                                       |                                                                                      
|Investments, Fair Value Disclosure                                                                                                                                    | 4,694                                                                                 |                                                                                      
|Level 2 [Member] | US Government Agency Debt Securities Commercial [Member]                                                                                           |                                                                                       |                                                                                      
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                      |                                                                                       |                                                                                      
|Investments, Fair Value Disclosure                                                                                                                                    | 308,870                                                                               |                                                                                      
|Level 2 [Member] | Residential Mortgage Backed Securities [Member]                                                                                                    |                                                                                       |                                                                                      
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                      |                                                                                       |                                                                                      
|Investments, Fair Value Disclosure                                                                                                                                    | 509,530                                                                               |                                                                                      
|Level 2 [Member] | Obligations of U.S. Government-Sponsored Enterprises - Other Government-Sponsored Enterprises [Member]                                             |                                                                                       |                                                                                      
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                      |                                                                                       |                                                                                      
|Investments, Fair Value Disclosure                                                                                                                                    | 919                                                                                   |                                                                                      
|Level 2 [Member] | Obligations of States and Political Subdivisions [Member]                                                                                          |                                                                                       |                                                                                      
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                      |                                                                                       |                                                                                      
|Investments, Fair Value Disclosure                                                                                                                                    | 8,591                                                                                 |                                                                                      
|Level 2 [Member] | Corporate Debt Securities [Member]                                                                                                                 |                                                                                       |                                                                                      
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                      |                                                                                       |                                                                                      
|Investments, Fair Value Disclosure                                                                                                                                    | 31,018                                                                                |                                                                                      
|Level 3 [Member]                                                                                                                                                      |                                                                                       |                                                                                      
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                      |                                                                                       |                                                                                      
|Other investments                                                                                                                                                     | 1,170                                                                                 |                                                                                      
|Loans Held for Sale                                                                                                                                                   | 0                                                                                     |                                                                                      
|Other Assets                                                                                                                                                          | 16,613                                                                                | [1]                                                                                  
|Total Assets                                                                                                                                                          | 17,783                                                                                |                                                                                      
|Other Liabilities                                                                                                                                                     | 0                                                                                     | [1]                                                                                  
|Total Liabilities                                                                                                                                                     | 0                                                                                     |                                                                                      
|Investments, Fair Value Disclosure                                                                                                                                    | 0                                                                                     |                                                                                      
|Level 3 [Member] | US Government Agencies Residential Mortgage-backed Securities [Member]                                                                             |                                                                                       |                                                                                      
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                      |                                                                                       |                                                                                      
|Investments, Fair Value Disclosure                                                                                                                                    | 0                                                                                     |                                                                                      
|Level 3 [Member] | US Government Agency Debt Securities Commercial [Member]                                                                                           |                                                                                       |                                                                                      
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                      |                                                                                       |                                                                                      
|Investments, Fair Value Disclosure                                                                                                                                    | 0                                                                                     |                                                                                      
|Level 3 [Member] | Residential Mortgage Backed Securities [Member]                                                                                                    |                                                                                       |                                                                                      
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                      |                                                                                       |                                                                                      
|Investments, Fair Value Disclosure                                                                                                                                    | 0                                                                                     |                                                                                      
|Level 3 [Member] | Obligations of U.S. Government-Sponsored Enterprises - Other Government-Sponsored Enterprises [Member]                                             |                                                                                       |                                                                                      
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                      |                                                                                       |                                                                                      
|Investments, Fair Value Disclosure                                                                                                                                    | 0                                                                                     |                                                                                      
|Level 3 [Member] | Obligations of States and Political Subdivisions [Member]                                                                                          |                                                                                       |                                                                                      
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                      |                                                                                       |                                                                                      
|Investments, Fair Value Disclosure                                                                                                                                    | 0                                                                                     |                                                                                      
|Level 3 [Member] | Corporate Debt Securities [Member]                                                                                                                 |                                                                                       |                                                                                      
|**Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                      |                                                                                       |                                                                                      
|Investments, Fair Value Disclosure                                                                                                                                    | $ 0                                                                                   |                                                                                      
|                                                                                                                                                                     
|[1]
Hedging and non-hedging interest rate derivatives and limited partnership investments[2]
on-hedging interest rate derivatives and limited partnership investments | [1]                                                                                   | Hedging and non-hedging interest rate derivatives and limited partnership investments
|[1]                                                                                                                                                                   | Hedging and non-hedging interest rate derivatives and limited partnership investments
|[2]                                                                                                                                                                   | on-hedging interest rate derivatives and limited partnership investments             

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