Investment Securities - Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Amortized Cost
Due after one year through five years	$ 99,992
Due after five years through ten years	64,726
Total contractual maturities	164,718
Mortgage- and asset-backed securities	4,389,883
Amortized Cost	4,554,601	$ 4,640,419
Fair Value
Due after one year through five years	98,193
Due after five years through ten years	63,402
Total contractual maturities	161,595
Mortgage- and asset-backed securities	4,324,065
Fair value	4,485,660	4,498,342
Government agency debt securities
Amortized Cost
Mortgage- and asset-backed securities	24,778
Amortized Cost	24,778
Fair Value
Mortgage- and asset-backed securities	24,765
Fair value	24,765
Government agency mortgage-backed securities
Amortized Cost
Mortgage- and asset-backed securities	377,960
Amortized Cost	377,960	426,710
Fair Value
Mortgage- and asset-backed securities	371,035
Fair value	371,035	411,536
Government-sponsored enterprises mortgage-backed securities
Amortized Cost
Mortgage- and asset-backed securities	131,884
Amortized Cost	131,884	156,056
Fair Value
Mortgage- and asset-backed securities	127,896
Fair value	127,896	150,847
Collateralized mortgage obligations: Government agency
Amortized Cost
Mortgage- and asset-backed securities	2,778,862
Amortized Cost	2,778,862	2,779,620
Fair Value
Mortgage- and asset-backed securities	2,730,166
Fair value	2,730,166	2,682,449
Collateralized mortgage obligations: Government-sponsored enterprises
Amortized Cost
Mortgage- and asset-backed securities	1,076,399
Amortized Cost	1,076,399	620,337
Fair Value
Mortgage- and asset-backed securities	1,070,203
Fair value	$ 1,070,203	$ 602,592

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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