Securities - Amortized Cost and Fair Value of Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Amortized Cost
Due within one year	$ 21,604
Due after one year through five years	30,383
Due after five years through ten years	76,550
Due after ten years	108,713
Amortized Cost	1,222,123	$ 1,264,529
Fair Value
Due within one year	21,839
Due after one year through five years	31,139
Due after five years through ten years	79,296
Due after ten years	108,264
Fair Value	1,238,577	1,250,777
Other debt securities
Amortized Cost
Debt securities, without fixed maturity, amortized cost	36,229
Amortized Cost	46,739	44,046
Fair Value
Debt securities, without fixed maturity, fair value	37,596
Fair Value	48,249	43,927
Government agency mortgage backed securities \| Residential mortgage backed securities
Amortized Cost
Debt securities, without fixed maturity, amortized cost	658,830
Amortized Cost	658,830	621,690
Fair Value
Debt securities, without fixed maturity, fair value	666,167
Fair Value	666,167	613,283
Government agency mortgage backed securities \| Commercial mortgage-backed securities
Amortized Cost
Debt securities, without fixed maturity, amortized cost	26,794
Amortized Cost	26,794	21,957
Fair Value
Debt securities, without fixed maturity, fair value	27,666
Fair Value	27,666	21,830
Government agency collateralized mortgage obligations \| Residential mortgage backed securities
Amortized Cost
Debt securities, without fixed maturity, amortized cost	189,332
Amortized Cost	189,332	332,697
Fair Value
Debt securities, without fixed maturity, fair value	191,187
Fair Value	191,187	326,989
Government agency collateralized mortgage obligations \| Commercial mortgage-backed securities
Amortized Cost
Debt securities, without fixed maturity, amortized cost	73,688
Amortized Cost	73,688	28,446
Fair Value
Debt securities, without fixed maturity, fair value	75,423
Fair Value	$ 75,423	$ 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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