Investment Securities - Amortized Cost and Fair Value, by Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Amortized Cost
Due after one year through five years	$ 38,268
Due after five years through ten years	3,277
Due after ten years	100,823
Total contractual maturities	142,368
Amortized Cost	5,584,556	$ 4,080,663
Fair Value
Due after one year through five years	38,863
Due after five years through ten years	3,280
Due after ten years	102,813
Total contractual maturities	144,956
Fair value	5,692,883	4,075,644
Mortgage-backed securities:
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	1,830,788
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	1,875,985
Residential - Government agency
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	188,797
Amortized Cost	188,797	290,131
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	193,948
Fair value	193,948	291,209
Residential - Government-sponsored enterprises
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	417,286
Amortized Cost	417,286	395,039
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	431,842
Fair value	431,842	399,492
Commercial - Government agency
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	737,891
Amortized Cost	737,891
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	751,922
Fair value	751,922
Commercial - Government-sponsored enterprises
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	486,814
Amortized Cost	486,814	101,798
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	498,273
Fair value	498,273	101,719
Collateralized mortgage obligations
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	3,611,400
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	3,671,942
Government agency
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	2,047,556
Amortized Cost	2,047,556	2,390,143
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	2,085,976
Fair value	2,085,976	2,381,278
Government-sponsored enterprises
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	1,563,844
Amortized Cost	1,563,844	772,023
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	1,585,966
Fair value	$ 1,585,966	$ 770,619

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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