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Fair Value Measurements and Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands | 6 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2018 | Dec. 31, 2017
Transfers between Levels [Abstract] |  |
Transfers from Level 1 to Level 2 | $ 0 | $ 0
Transfers from Level 2 to Level 1 | 4,000 | 0
Transfers into Level 3 |  | 0
Transfers out of Level 3 |  | 0
AFS securities [Abstract] |  |
AFS securities | 1,192,939 |
Total AFS securities | 1,192,939 | 1,255,925
Equity securities | 24,293 | 0
Trading securities | 0 | 11,467
Liabilities [Abstract] |  |
Collateral dependent loans | 25 | 100
Collateral dependent loans, specific reserves | $ 25 | 100
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] |  |
AFS securities | $ 118,570 | 108,899
State & Municipal [Member] |  |
AFS securities [Abstract] |  |
AFS securities | 36,402 | 41,956
Recurring Basis [Member] |  |
AFS securities [Abstract] |  |
AFS securities | 1,192,939 |
Other securities |  | 14,149
Total AFS securities |  | 1,255,925
Equity securities | 24,293 |
Trading securities |  | 11,467
Derivatives | 22,568 | 3,732
Total | 1,239,800 | 1,271,124
Liabilities [Abstract] |  |
Derivatives | 18,463 | 324
Total | 18,463 | 324
Recurring Basis [Member] | Level 1 [Member] |  |
AFS securities [Abstract] |  |
AFS securities | 0 |
Other securities |  | 5,845
Total AFS securities |  | 5,845
Equity securities | 20,109 |
Trading securities |  | 11,467
Derivatives | 0 | 0
Total | 20,109 | 17,312
Liabilities [Abstract] |  |
Derivatives | 0 | 0
Total | 0 | 0
Recurring Basis [Member] | Level 2 [Member] |  |
AFS securities [Abstract] |  |
AFS securities | 1,192,939 |
Other securities |  | 8,304
Total AFS securities |  | 1,250,080
Equity securities | 4,184 |
Trading securities |  | 0
Derivatives | 22,568 | 3,732
Total | 1,219,691 | 1,253,812
Liabilities [Abstract] |  |
Derivatives | 18,463 | 324
Total | 18,463 | 324
Recurring Basis [Member] | Level 3 [Member] |  |
AFS securities [Abstract] |  |
AFS securities | 0 |
Other securities |  | 0
Total AFS securities |  | 0
Equity securities | 0 |
Trading securities |  | 0
Derivatives | 0 | 0
Total | 0 | 0
Liabilities [Abstract] |  |
Derivatives | 0 | 0
Total | 0 | 0
Recurring Basis [Member] | Federal Agency [Member] |  |
AFS securities [Abstract] |  |
AFS securities | 118,570 | 108,899
Recurring Basis [Member] | Federal Agency [Member] | Level 1 [Member] |  |
AFS securities [Abstract] |  |
AFS securities | 0 | 0
Recurring Basis [Member] | Federal Agency [Member] | Level 2 [Member] |  |
AFS securities [Abstract] |  |
AFS securities | 118,570 | 108,899
Recurring Basis [Member] | Federal Agency [Member] | Level 3 [Member] |  |
AFS securities [Abstract] |  |
AFS securities | 0 | 0
Recurring Basis [Member] | State & Municipal [Member] |  |
AFS securities [Abstract] |  |
AFS securities | 36,402 | 41,956
Recurring Basis [Member] | State & Municipal [Member] | Level 1 [Member] |  |
AFS securities [Abstract] |  |
AFS securities | 0 | 0
Recurring Basis [Member] | State & Municipal [Member] | Level 2 [Member] |  |
AFS securities [Abstract] |  |
AFS securities | 36,402 | 41,956
Recurring Basis [Member] | State & Municipal [Member] | Level 3 [Member] |  |
AFS securities [Abstract] |  |
AFS securities | 0 | 0
Recurring Basis [Member] | Mortgage-Backed [Member] |  |
AFS securities [Abstract] |  |
AFS securities | 519,645 | 554,927
Recurring Basis [Member] | Mortgage-Backed [Member] | Level 1 [Member] |  |
AFS securities [Abstract] |  |
AFS securities | 0 | 0
Recurring Basis [Member] | Mortgage-Backed [Member] | Level 2 [Member] |  |
AFS securities [Abstract] |  |
AFS securities | 519,645 | 554,927
Recurring Basis [Member] | Mortgage-Backed [Member] | Level 3 [Member] |  |
AFS securities [Abstract] |  |
AFS securities | 0 | 0
Recurring Basis [Member] | Collateralized Mortgage Obligations [Member] |  |
AFS securities [Abstract] |  |
AFS securities | 518,322 | 535,994
Recurring Basis [Member] | Collateralized Mortgage Obligations [Member] | Level 1 [Member] |  |
AFS securities [Abstract] |  |
AFS securities | 0 | 0
Recurring Basis [Member] | Collateralized Mortgage Obligations [Member] | Level 2 [Member] |  |
AFS securities [Abstract] |  |
AFS securities | 518,322 | 535,994
Recurring Basis [Member] | Collateralized Mortgage Obligations [Member] | Level 3 [Member] |  |
AFS securities [Abstract] |  |
AFS securities | $ 0 | $ 0

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