Securities - Amortized Cost and Fair Value of Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Amortized Cost
Due within one year	$ 36,647
Due after one year through five years	40,168
Due after five years through ten years	74,651
Due after ten years	51,868
Amortized Cost	1,253,939	$ 1,264,529
Fair Value
Due within one year	36,919
Due after one year through five years	40,856
Due after five years through ten years	76,630
Due after ten years	50,926
Fair Value	1,255,353	1,250,777
Other debt securities
Amortized Cost
Debt securities, without fixed maturity, amortized cost	39,550
Amortized Cost	48,335	44,046
Fair Value
Debt securities, without fixed maturity, fair value	40,181
Fair Value	48,979	43,927
Government agency mortgage backed securities \| Residential mortgage backed securities
Amortized Cost
Debt securities, without fixed maturity, amortized cost	622,056
Amortized Cost	622,056	621,690
Fair Value
Debt securities, without fixed maturity, fair value	622,066
Fair Value	622,066	613,283
Government agency mortgage backed securities \| Commercial mortgage-backed securities
Amortized Cost
Debt securities, without fixed maturity, amortized cost	21,816
Amortized Cost	21,816	21,957
Fair Value
Debt securities, without fixed maturity, fair value	21,998
Fair Value	21,998	21,830
Government agency collateralized mortgage obligations \| Residential mortgage backed securities
Amortized Cost
Debt securities, without fixed maturity, amortized cost	321,088
Amortized Cost	321,088	332,697
Fair Value
Debt securities, without fixed maturity, fair value	319,447
Fair Value	319,447	326,989
Government agency collateralized mortgage obligations \| Commercial mortgage-backed securities
Amortized Cost
Debt securities, without fixed maturity, amortized cost	46,095
Amortized Cost	46,095	28,446
Fair Value
Debt securities, without fixed maturity, fair value	46,330
Fair Value	$ 46,330	$ 28,335

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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