Investment Securities - Amortized Cost and Fair Value, by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Amortized Cost
Due after one year through five years	$ 41,513
Due after five years through ten years	83,988
Due after ten years	52,244
Total contractual maturities	177,745
Amortized Cost	6,708,431	$ 5,985,031
Fair Value
Due after one year through five years	41,878
Due after five years through ten years	83,461
Due after ten years	50,385
Total contractual maturities	175,724
Fair value	6,692,479	6,071,415
Mortgage-backed securities:
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	2,630,661
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	2,596,505
Residential - Government agency
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	129,908
Amortized Cost	129,908	155,169
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	133,894
Fair value	133,894	160,462
Residential - Government-sponsored enterprises
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	797,426
Amortized Cost	797,426	434,282
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	800,920
Fair value	800,920	447,200
Commercial - Government agency
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	523,293
Amortized Cost	523,293	583,232
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	527,516
Fair value	527,516	599,650
Commercial - Government-sponsored enterprises
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	1,180,034
Amortized Cost	1,180,034	931,095
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	1,134,175
Fair value	1,134,175	932,157
Collateralized mortgage obligations
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	3,900,025
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	3,920,250
Government agency
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	1,818,181
Amortized Cost	1,818,181	1,902,326
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	1,845,098
Fair value	1,845,098	1,933,553
Government-sponsored enterprises
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	2,081,844
Amortized Cost	2,081,844	1,808,804
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	2,075,152
Fair value	$ 2,075,152	$ 1,826,972

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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