Investment Securities - Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Amortized Cost
Due after one year through five years	$ 503,416
Due after five years through ten years	149,725
Due after ten years	20,344
Total contractual maturities	673,485
Mortgage- and asset-backed securities	4,166,503
Amortized Cost	4,839,988	$ 5,357,275
Fair Value
Due after one year through five years	479,725
Due after five years through ten years	141,382
Due after ten years	19,563
Total contractual maturities	640,670
Mortgage- and asset-backed securities	3,954,631
Fair value	4,595,301	5,234,658
Government agency mortgage-backed securities
Amortized Cost
Mortgage- and asset-backed securities	439,773
Amortized Cost	439,773	356,858
Fair Value
Mortgage- and asset-backed securities	419,293
Fair value	419,293	351,390
Government-sponsored enterprises mortgage-backed securities
Amortized Cost
Mortgage- and asset-backed securities	161,975
Amortized Cost	161,975	178,702
Fair Value
Mortgage- and asset-backed securities	154,133
Fair value	154,133	174,741
Collateralized mortgage obligations: Government agency
Amortized Cost
Mortgage- and asset-backed securities	2,906,962
Amortized Cost	2,906,962	3,367,173
Fair Value
Mortgage- and asset-backed securities	2,753,966
Fair value	2,753,966	3,290,474
Collateralized mortgage obligations: Government-sponsored enterprises
Amortized Cost
Mortgage- and asset-backed securities	657,793
Amortized Cost	657,793	779,911
Fair Value
Mortgage- and asset-backed securities	627,239
Fair value	$ 627,239	$ 762,718

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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