Investment Securities - Summary of Available-for-Sale Debt Securities by Stated Maturity (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Due in one year or less, amortized cost	$ 4,992
Due after one years through five years, amortized cost	419,539
Due after five through ten years, amortized cost	191,230
Amortized Cost	4,232,729	$ 3,799,851
Due in one year or less, fair value	4,999
Due after one years through five years, fair value	409,141
Due after five through ten years, fair value	187,560
Total Debt Securities Fair Value	4,144,029	3,791,575
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, without single maturity date, amortized cost	351,847
Amortized Cost	351,847	297,291
Debt securities, available-for-sale, without single maturity date, fair value	343,619
Total Debt Securities Fair Value	343,619	297,425
Collateralized loan obligations
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, without single maturity date, amortized cost	1,010,938
Amortized Cost	1,010,938	1,067,770
Debt securities, available-for-sale, without single maturity date, fair value	1,004,362
Total Debt Securities Fair Value	1,004,362	1,066,802
Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, without single maturity date, amortized cost	148,993
Amortized Cost	148,993	149,054
Debt securities, available-for-sale, without single maturity date, fair value	147,625
Total Debt Securities Fair Value	147,625	148,927
Agency-guaranteed residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, without single maturity date, amortized cost	9,242
Amortized Cost	9,242	9,865
Debt securities, available-for-sale, without single maturity date, fair value	8,269
Total Debt Securities Fair Value	8,269	9,553
Agency-guaranteed commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, without single maturity date, amortized cost	2,140
Amortized Cost	2,140	2,162
Debt securities, available-for-sale, without single maturity date, fair value	2,045
Total Debt Securities Fair Value	2,045	2,152
Agency-guaranteed residential collateralized mortgage obligations
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, without single maturity date, amortized cost	618,998
Amortized Cost	618,998	199,091
Debt securities, available-for-sale, without single maturity date, fair value	603,403
Total Debt Securities Fair Value	603,403	196,930
Agency-guaranteed commercial collateralized mortgage obligations
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, without single maturity date, amortized cost	172,410
Amortized Cost	172,410	242,668
Debt securities, available-for-sale, without single maturity date, fair value	162,599
Total Debt Securities Fair Value	162,599	238,844
Private label collateralized mortgage obligations
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, without single maturity date, amortized cost	1,302,400
Amortized Cost	1,302,400	1,248,142
Debt securities, available-for-sale, without single maturity date, fair value	1,270,407
Total Debt Securities Fair Value	$ 1,270,407	$ 1,242,465

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in sixth through tenth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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