| **Investment Securities - Amortized Cost and Fair Values of Debt Securities Held to Maturity (Details) - USD ($) $ in Thousands** | Dec. 31, 2018 | Dec. 31, 2017 |
|-----------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Schedule of Held-to-maturity Securities [Line Items]**                                                                          |          |          |
| Amortized Cost                                                                                                                    | $ 393,855     | $ 422,096     |
| Gross Unrealized Gains                                                                                                            | 387           | 345           |
| Gross Unrealized Losses                                                                                                           | (10,249)      | (4,192)       |
| Estimated Fair Value                                                                                                              | 383,993       | 418,249       |
| Obligations of U.S. Government-Sponsored Enterprises [Member]                                                                     |          |          |
| **Schedule of Held-to-maturity Securities [Line Items]**                                                                          |          |          |
| Amortized Cost                                                                                                                    | 42,331        | 40,540        |
| Gross Unrealized Gains                                                                                                            | 175           | 335           |
| Gross Unrealized Losses                                                                                                           | (313)         | (161)         |
| Estimated Fair Value                                                                                                              | 42,193        | 40,714        |
| ERROR in label resolution.                                                                                                        |          |          |
| **Schedule of Held-to-maturity Securities [Line Items]**                                                                          |          |          |
| Amortized Cost                                                                                                                    | 400           | 200           |
| Gross Unrealized Gains                                                                                                            | 0             | 0             |
| Gross Unrealized Losses                                                                                                           | 0             | 0             |
| Estimated Fair Value                                                                                                              | 400           | 200           |
| Mortgage - Backed Securities - Commercial [Member] | Obligations of U.S. Government [Member]                                      |          |          |
| **Schedule of Held-to-maturity Securities [Line Items]**                                                                          |          |          |
| Amortized Cost                                                                                                                    | 55,221        | 58,249        |
| Gross Unrealized Gains                                                                                                            | 0             | 0             |
| Gross Unrealized Losses                                                                                                           | (2,327)       | (1,394)       |
| Estimated Fair Value                                                                                                              | 52,894        | 56,855        |
| Mortgage - Backed Securities - Commercial [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member]                |          |          |
| **Schedule of Held-to-maturity Securities [Line Items]**                                                                          |          |          |
| Amortized Cost                                                                                                                    | 13,159        | 14,056        |
| Gross Unrealized Gains                                                                                                            | 0             | 0             |
| Gross Unrealized Losses                                                                                                           | (258)         | (71)          |
| Estimated Fair Value                                                                                                              | 12,901        | 13,985        |
| Mortgage - Backed Securities - Residential [Member] | Obligations of U.S. Government [Member]                                     |          |          |
| **Schedule of Held-to-maturity Securities [Line Items]**                                                                          |          |          |
| Amortized Cost                                                                                                                    | 3,635         | 3,925         |
| Gross Unrealized Gains                                                                                                            | 0             | 0             |
| Gross Unrealized Losses                                                                                                           | (97)          | (14)          |
| Estimated Fair Value                                                                                                              | 3,538         | 3,911         |
| Mortgage - Backed Securities - Residential [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member]               |          |          |
| **Schedule of Held-to-maturity Securities [Line Items]**                                                                          |          |          |
| Amortized Cost                                                                                                                    | 279,109       | 305,126       |
| Gross Unrealized Gains                                                                                                            | 212           | 10            |
| Gross Unrealized Losses                                                                                                           | (7,254)       | (2,552)       |
| Estimated Fair Value                                                                                                              | $ 272,067     | $ 302,584     |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of investment in debt security measured at amortized cost (held-to-maturity).
+ References
Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563
+ Details**Name:**us-gaap_HeldToMaturitySecurities**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).
+ References
Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563
+ Details**Name:**us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).
+ References
Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563
+ Details**Name:**us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair value of investment in debt security measured at amortized cost (held-to-maturity).
+ References
Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563
+ Details**Name:**us-gaap_HeldToMaturitySecuritiesFairValue**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
+ References
No definition available.
+ Details**Name:**us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                    |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancialInstrumentAxis=us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                     |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancialInstrumentAxis=us-gaap_ForeignGovernmentDebtSecuritiesMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                              |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FairValueByLiabilityClassAxis=us-gaap_CommercialMortgageBackedSecuritiesMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                             |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancialInstrumentAxis=us-gaap_USTreasuryAndGovernmentMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                               |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FairValueByLiabilityClassAxis=us-gaap_ResidentialMortgageBackedSecuritiesMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |