Securities - Amortized Cost and Fair Value of Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Amortized Cost
Due within one year	$ 10,286
Due after one year through five years	40,177
Due after five years through ten years	66,563
Due after ten years	235,945
Amortized Cost	1,515,958	$ 1,301,973
Fair Value
Due within one year	10,401
Due after one year through five years	41,896
Due after five years through ten years	69,568
Due after ten years	239,498
Fair Value	1,536,041	1,343,457
Other debt securities
Amortized Cost
Debt securities, without fixed maturity, amortized cost	33,327
Amortized Cost	61,113	62,771
Fair Value
Debt securities, without fixed maturity, fair value	34,708
Fair Value	63,199	65,607
Government agency mortgage backed securities \| Residential mortgage backed securities:
Amortized Cost
Debt securities, without fixed maturity, amortized cost	453,792
Amortized Cost	453,792	581,105
Fair Value
Debt securities, without fixed maturity, fair value	466,455
Fair Value	466,455	602,646
Government agency mortgage backed securities \| Commercial mortgage backed securities:
Amortized Cost
Debt securities, without fixed maturity, amortized cost	22,448
Amortized Cost	22,448	29,053
Fair Value
Debt securities, without fixed maturity, fair value	23,005
Fair Value	23,005	30,287
Government agency collateralized mortgage obligations \| Residential mortgage backed securities:
Amortized Cost
Debt securities, without fixed maturity, amortized cost	538,317
Amortized Cost	538,317	218,373
Fair Value
Debt securities, without fixed maturity, fair value	535,332
Fair Value	535,332	220,268
Government agency collateralized mortgage obligations \| Commercial mortgage backed securities:
Amortized Cost
Debt securities, without fixed maturity, amortized cost	115,103
Amortized Cost	115,103	99,377
Fair Value
Debt securities, without fixed maturity, fair value	115,178
Fair Value	$ 115,178	$ 102,348

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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