Investment Securities - Amortized Cost and Fair Value, by Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Amortized Cost
Due after one year through five years	$ 41,481
Due after five years through ten years	83,227
Due after ten years	64,153
Total contractual maturities	188,861
Amortized Cost	7,994,266	$ 5,985,031
Fair Value
Due after one year through five years	41,777
Due after five years through ten years	82,733
Due after ten years	63,351
Total contractual maturities	187,861
Fair value	7,953,727	6,071,415
Mortgage-backed securities:
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	3,337,784
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	3,306,855
Residential - Government agency
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	95,337
Amortized Cost	95,337	155,169
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	98,134
Fair value	98,134	160,462
Residential - Government-sponsored enterprises
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	1,455,375
Amortized Cost	1,455,375	434,282
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	1,458,878
Fair value	1,458,878	447,200
Commercial - Government agency
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	449,147
Amortized Cost	449,147	583,232
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	448,594
Fair value	448,594	599,650
Commercial - Government-sponsored enterprises
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	1,337,925
Amortized Cost	1,337,925	931,095
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	1,301,249
Fair value	1,301,249	932,157
Collateralized mortgage obligations
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	4,467,621
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	4,459,011
Government agency
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	2,053,171
Amortized Cost	2,053,171	1,902,326
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	2,059,864
Fair value	2,059,864	1,933,553
Government-sponsored enterprises
Amortized Cost
Mortgaged-backed securities and collateralized mortgage obligations	2,414,450
Amortized Cost	2,414,450	1,808,804
Fair Value
Mortgaged-backed securities and collateralized mortgage obligations	2,399,147
Fair value	$ 2,399,147	$ 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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