| **Loans and Allowance - Allowance for Credit Losses and Loan Portfolio by Loan Segment (Details) - USD ($) $ in Thousands** | Sep. 30, 2018 | Jun. 30, 2018 | Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Dec. 31, 2016 |
|-----------------------------------------------------------------------------------------------------------------------------|---------------|---------------|---------------|---------------|---------------|---------------|
| **Allowance Balances:**                                                                                                     |          |          |          |          |          |          |
| Individually evaluated for impairment                                                                                       | $ 433         |          | $ 1,637       |          |          |          |
| Collectively evaluated for impairment                                                                                       | 77,973        |          | 73,395        |          |          |          |
| Total Allowance for Loan Losses                                                                                             | 78,406        | $ 77,543      | 75,032        | $ 73,354      | $ 70,471      | $ 66,037      |
| **Loan Balance [Abstract]**                                                                                                 |          |          |          |          |          |          |
| Individually evaluated for impairment                                                                                       | 15,999        |          | 23,211        |          |          |          |
| Collectively evaluated for impairment                                                                                       | 7,052,993     |          | 6,703,034     |          |          |          |
| Loans                                                                                                                       | 7,088,071     |          | 6,751,199     |          |          |          |
| Loans acquired with deteriorated credit quality                                                                             |          |          |          |          |          |          |
| **Loan Balance [Abstract]**                                                                                                 |          |          |          |          |          |          |
| Loans                                                                                                                       | 19,079        |          | 24,954        |          |          |          |
| Commercial                                                                                                                  |          |          |          |          |          |          |
| **Allowance Balances:**                                                                                                     |          |          |          |          |          |          |
| Individually evaluated for impairment                                                                                       |               |          | 666           |          |          |          |
| Collectively evaluated for impairment                                                                                       | 32,066        |          | 29,752        |          |          |          |
| Total Allowance for Loan Losses                                                                                             | 32,066        | 31,465        | 30,418        | 29,683        | 28,906        | 27,696        |
| **Loan Balance [Abstract]**                                                                                                 |          |          |          |          |          |          |
| Individually evaluated for impairment                                                                                       | 1,614         |          | 3,345         |          |          |          |
| Collectively evaluated for impairment                                                                                       | 2,132,193     |          | 2,005,275     |          |          |          |
| Loans                                                                                                                       | 2,136,099     |          | 2,010,041     |          |          |          |
| Commercial | Loans acquired with deteriorated credit quality                                                                |          |          |          |          |          |          |
| **Loan Balance [Abstract]**                                                                                                 |          |          |          |          |          |          |
| Loans                                                                                                                       | 2,292         |          | 1,421         |          |          |          |
| Commercial Real Estate                                                                                                      |          |          |          |          |          |          |
| **Allowance Balances:**                                                                                                     |          |          |          |          |          |          |
| Individually evaluated for impairment                                                                                       |               |          | 567           |          |          |          |
| Collectively evaluated for impairment                                                                                       | 27,946        |          | 26,776        |          |          |          |
| Total Allowance for Loan Losses                                                                                             | 27,946        | 27,731        | 27,343        | 26,747        | 25,236        | 23,661        |
| **Loan Balance [Abstract]**                                                                                                 |          |          |          |          |          |          |
| Individually evaluated for impairment                                                                                       | 12,158        |          | 17,432        |          |          |          |
| Collectively evaluated for impairment                                                                                       | 3,340,898     |          | 3,135,481     |          |          |          |
| Loans                                                                                                                       | 3,368,237     |          | 3,174,910     |          |          |          |
| Commercial Real Estate | Loans acquired with deteriorated credit quality                                                    |          |          |          |          |          |          |
| **Loan Balance [Abstract]**                                                                                                 |          |          |          |          |          |          |
| Loans                                                                                                                       | 15,181        |          | 21,997        |          |          |          |
| Consumer                                                                                                                    |          |          |          |          |          |          |
| **Allowance Balances:**                                                                                                     |          |          |          |          |          |          |
| Individually evaluated for impairment                                                                                       |               |          |               |          |          |          |
| Collectively evaluated for impairment                                                                                       | 3,932         |          | 3,732         |          |          |          |
| Total Allowance for Loan Losses                                                                                             | 3,932         | 3,921         | 3,732         | 3,591         | 3,372         | 2,923         |
| **Loan Balance [Abstract]**                                                                                                 |          |          |          |          |          |          |
| Individually evaluated for impairment                                                                                       | 8             |          | 5             |          |          |          |
| Collectively evaluated for impairment                                                                                       | 98,701        |          | 86,930        |          |          |          |
| Loans                                                                                                                       | 98,709        |          | 86,935        |          |          |          |
| Consumer | Loans acquired with deteriorated credit quality                                                                  |          |          |          |          |          |          |
| **Loan Balance [Abstract]**                                                                                                 |          |          |          |          |          |          |
| Loans                                                                                                                       |               |          |               |          |          |          |
| Residential                                                                                                                 |          |          |          |          |          |          |
| **Allowance Balances:**                                                                                                     |          |          |          |          |          |          |
| Individually evaluated for impairment                                                                                       | 433           |          | 404           |          |          |          |
| Collectively evaluated for impairment                                                                                       | 14,027        |          | 13,133        |          |          |          |
| Total Allowance for Loan Losses                                                                                             | 14,460        | 14,424        | 13,537        | 13,331        | 12,955        | 11,755        |
| **Loan Balance [Abstract]**                                                                                                 |          |          |          |          |          |          |
| Individually evaluated for impairment                                                                                       | 2,219         |          | 2,429         |          |          |          |
| Collectively evaluated for impairment                                                                                       | 1,479,371     |          | 1,472,821     |          |          |          |
| Loans                                                                                                                       | 1,483,196     |          | 1,476,786     |          |          |          |
| Residential | Loans acquired with deteriorated credit quality                                                               |          |          |          |          |          |          |
| **Loan Balance [Abstract]**                                                                                                 |          |          |          |          |          |          |
| Loans                                                                                                                       | 1,606         |          | 1,536         |          |          |          |
| Lease financing receivables, net of unearned income                                                                         |          |          |          |          |          |          |
| **Allowance Balances:**                                                                                                     |          |          |          |          |          |          |
| Individually evaluated for impairment                                                                                       |               |          |               |          |          |          |
| Collectively evaluated for impairment                                                                                       | 2             |          | 2             |          |          |          |
| Total Allowance for Loan Losses                                                                                             | 2             | $ 2           | 2             | $ 2           | $ 2           | $ 2           |
| **Loan Balance [Abstract]**                                                                                                 |          |          |          |          |          |          |
| Individually evaluated for impairment                                                                                       |               |          |               |          |          |          |
| Collectively evaluated for impairment                                                                                       | 1,830         |          | 2,527         |          |          |          |
| Loans                                                                                                                       | 1,830         |          | 2,527         |          |          |          |
| Lease financing receivables, net of unearned income | Loans acquired with deteriorated credit quality                       |          |          |          |          |          |          |
| **Loan Balance [Abstract]**                                                                                                 |          |          |          |          |          |          |
| Loans                                                                                                                       |               |          |               |          |          |          |

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| - Definition
The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.
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| - Definition
Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.
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The balance of financing receivables that were collectively evaluated for impairment.
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The balance of financing receivables that were individually evaluated for impairment.
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| - Definition
Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.
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