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Fair Value Measurements and Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Mar. 31, 2017 | Dec. 31, 2016 | Mar. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Fair Value, Assets, Level 1 to Level 2 Transfers, Amount | $ 0 | $ 0 |
Fair Value, Assets, Level 2 to Level 1 Transfers, Amount | 0 | 0 |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 | 0 | 0 |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 | 0 | 0 |
AFS securities [Abstract] |  |  |
Securities available for sale, at estimated fair value | 1,367,574 | 1,338,290 |
Trading securities | 10,044 | 9,259 |
Liabilities [Abstract] |  |  |
Collateral dependent impaired financing receivable with specific reserves | 1,200 |  | $ 9,000
Allowance for loan losses for collateral dependent impaired loans with specific reserves | $ 400 |  | $ 3,000
Minimum [Member] |  |  |
Liabilities [Abstract] |  |  |
Liquidation expense ratio on impaired collateral | 10.00% |  |
Maximum [Member] |  |  |
Liabilities [Abstract] |  |  |
Liquidation expense ratio on impaired collateral | 35.00% |  |
Federal Agency [Member] |  |  |
AFS securities [Abstract] |  |  |
Securities available for sale, at estimated fair value | $ 159,581 | 174,408 |
State & Municipal [Member] |  |  |
AFS securities [Abstract] |  |  |
Securities available for sale, at estimated fair value | 47,844 | 46,726 |
Other Securities [Member] |  |  |
AFS securities [Abstract] |  |  |
Securities available for sale, at estimated fair value | 19,141 | 20,739 |
Recurring Basis [Member] |  |  |
AFS securities [Abstract] |  |  |
Securities available for sale, at estimated fair value | 1,367,574 | 1,338,290 |
Trading securities | 10,044 | 9,259 |
Interest rate swaps | 3,971 | 3,210 |
Total | 1,381,589 | 1,350,759 |
Liabilities [Abstract] |  |  |
Interest rate swaps | 736 | 506 |
Total | 736 | 506 |
Recurring Basis [Member] | Level 1 [Member] |  |  |
AFS securities [Abstract] |  |  |
Securities available for sale, at estimated fair value | 10,923 | 11,493 |
Trading securities | 10,044 | 9,259 |
Interest rate swaps | 0 | 0 |
Total | 20,967 | 20,752 |
Liabilities [Abstract] |  |  |
Interest rate swaps | 0 | 0 |
Total | 0 | 0 |
Recurring Basis [Member] | Level 2 [Member] |  |  |
AFS securities [Abstract] |  |  |
Securities available for sale, at estimated fair value | 1,356,651 | 1,326,797 |
Trading securities | 0 | 0 |
Interest rate swaps | 3,971 | 3,210 |
Total | 1,360,622 | 1,330,007 |
Liabilities [Abstract] |  |  |
Interest rate swaps | 736 | 506 |
Total | 736 | 506 |
Recurring Basis [Member] | Level 3 [Member] |  |  |
AFS securities [Abstract] |  |  |
Securities available for sale, at estimated fair value | 0 | 0 |
Trading securities | 0 | 0 |
Interest rate swaps | 0 | 0 |
Total | 0 | 0 |
Liabilities [Abstract] |  |  |
Interest rate swaps | 0 | 0 |
Total | 0 | 0 |
Recurring Basis [Member] | Federal Agency [Member] |  |  |
AFS securities [Abstract] |  |  |
Securities available for sale, at estimated fair value | 159,581 | 174,408 |
Recurring Basis [Member] | Federal Agency [Member] | Level 1 [Member] |  |  |
AFS securities [Abstract] |  |  |
Securities available for sale, at estimated fair value | 0 | 0 |
Recurring Basis [Member] | Federal Agency [Member] | Level 2 [Member] |  |  |
AFS securities [Abstract] |  |  |
Securities available for sale, at estimated fair value | 159,581 | 174,408 |
Recurring Basis [Member] | Federal Agency [Member] | Level 3 [Member] |  |  |
AFS securities [Abstract] |  |  |
Securities available for sale, at estimated fair value | 0 | 0 |
Recurring Basis [Member] | State & Municipal [Member] |  |  |
AFS securities [Abstract] |  |  |
Securities available for sale, at estimated fair value | 47,844 | 46,726 |
Recurring Basis [Member] | State & Municipal [Member] | Level 1 [Member] |  |  |
AFS securities [Abstract] |  |  |
Securities available for sale, at estimated fair value | 0 | 0 |
Recurring Basis [Member] | State & Municipal [Member] | Level 2 [Member] |  |  |
AFS securities [Abstract] |  |  |
Securities available for sale, at estimated fair value | 47,844 | 46,726 |
Recurring Basis [Member] | State & Municipal [Member] | Level 3 [Member] |  |  |
AFS securities [Abstract] |  |  |
Securities available for sale, at estimated fair value | 0 | 0 |
Recurring Basis [Member] | Mortgage-Backed [Member] |  |  |
AFS securities [Abstract] |  |  |
Securities available for sale, at estimated fair value | 578,027 | 529,844 |
Recurring Basis [Member] | Mortgage-Backed [Member] | Level 1 [Member] |  |  |
AFS securities [Abstract] |  |  |
Securities available for sale, at estimated fair value | 0 | 0 |
Recurring Basis [Member] | Mortgage-Backed [Member] | Level 2 [Member] |  |  |
AFS securities [Abstract] |  |  |
Securities available for sale, at estimated fair value | 578,027 | 529,844 |
Recurring Basis [Member] | Mortgage-Backed [Member] | Level 3 [Member] |  |  |
AFS securities [Abstract] |  |  |
Securities available for sale, at estimated fair value | 0 | 0 |
Recurring Basis [Member] | Collateralized Mortgage Obligations [Member] |  |  |
AFS securities [Abstract] |  |  |
Securities available for sale, at estimated fair value | 562,981 | 566,573 |
Recurring Basis [Member] | Collateralized Mortgage Obligations [Member] | Level 1 [Member] |  |  |
AFS securities [Abstract] |  |  |
Securities available for sale, at estimated fair value | 0 | 0 |
Recurring Basis [Member] | Collateralized Mortgage Obligations [Member] | Level 2 [Member] |  |  |
AFS securities [Abstract] |  |  |
Securities available for sale, at estimated fair value | 562,981 | 566,573 |
Recurring Basis [Member] | Collateralized Mortgage Obligations [Member] | Level 3 [Member] |  |  |
AFS securities [Abstract] |  |  |
Securities available for sale, at estimated fair value | 0 | 0 |
Recurring Basis [Member] | Other Securities [Member] |  |  |
AFS securities [Abstract] |  |  |
Securities available for sale, at estimated fair value | 19,141 | 20,739 |
Recurring Basis [Member] | Other Securities [Member] | Level 1 [Member] |  |  |
AFS securities [Abstract] |  |  |
Securities available for sale, at estimated fair value | 10,923 | 11,493 |
Recurring Basis [Member] | Other Securities [Member] | Level 2 [Member] |  |  |
AFS securities [Abstract] |  |  |
Securities available for sale, at estimated fair value | 8,218 | 9,246 |
Recurring Basis [Member] | Other Securities [Member] | Level 3 [Member] |  |  |
AFS securities [Abstract] |  |  |
Securities available for sale, at estimated fair value | $ 0 | $ 0 |

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