Securities - Amortized Cost and Fair Value of Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Amortized Cost
Due within one year	$ 19,647
Due after one year through five years	34,038
Due after five years through ten years	81,750
Due after ten years	160,241
Amortized Cost	1,322,998	$ 1,276,871
Fair Value
Due within one year	19,786
Due after one year through five years	34,948
Due after five years through ten years	84,830
Due after ten years	157,388
Fair Value	1,359,129	1,290,613
Other debt securities
Amortized Cost
Debt securities, without fixed maturity, amortized cost	39,888
Amortized Cost	56,380	55,364
Fair Value
Debt securities, without fixed maturity, fair value	41,182
Fair Value	57,812	56,365
Government agency mortgage backed securities \| Residential mortgage backed securities:
Amortized Cost
Debt securities, without fixed maturity, amortized cost	709,117
Amortized Cost	709,117	708,970
Fair Value
Debt securities, without fixed maturity, fair value	733,413
Fair Value	733,413	716,105
Government agency mortgage backed securities \| Commercial mortgage backed securities:
Amortized Cost
Debt securities, without fixed maturity, amortized cost	32,625
Amortized Cost	32,625	30,372
Fair Value
Debt securities, without fixed maturity, fair value	34,590
Fair Value	34,590	31,007
Government agency collateralized mortgage obligations \| Residential mortgage backed securities:
Amortized Cost
Debt securities, without fixed maturity, amortized cost	159,940
Amortized Cost	159,940	172,178
Fair Value
Debt securities, without fixed maturity, fair value	164,593
Fair Value	164,593	173,238
Government agency collateralized mortgage obligations \| Commercial mortgage backed securities:
Amortized Cost
Debt securities, without fixed maturity, amortized cost	85,752
Amortized Cost	85,752	76,456
Fair Value
Debt securities, without fixed maturity, fair value	88,399
Fair Value	$ 88,399	$ 77,751

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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