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Investment Securities - Amortized Cost and Estimated Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021
AFS investment securities:
Amortized Cost	$ 2,286,536		$ 2,904,745
Gross Unrealized Gain	104		0
Gross Unrealized Loss	(274,849)		(303,732)
Estimated Fair Value	2,011,791		2,601,013
HTM investment securities:
Amortized Cost	1,737,717		1,388,146
Allowance for Credit Losses	(113)	$ (227)	(43)	$ (109)	$ (41)	$ (22)
Net Carrying Amount	1,737,604		1,388,103
Gross Unrecognized Gain	70		44
Gross Unrecognized Loss	(279,387)		(291,051)
Estimated Fair Value	1,458,287		1,097,096
U.S. Treasury
AFS investment securities:
Amortized Cost	14,944		49,156
Gross Unrealized Gain	0		0
Gross Unrealized Loss	(1,840)		(2,139)
Estimated Fair Value	13,104		47,017
Agency
AFS investment securities:
Amortized Cost	463,958		485,331
Gross Unrealized Gain	0		0
Gross Unrealized Loss	(50,103)		(53,893)
Estimated Fair Value	413,855		431,438
Corporate
AFS investment securities:
Amortized Cost	561,128		586,652
Gross Unrealized Gain	104		0
Gross Unrealized Loss	(63,113)		(44,104)
Estimated Fair Value	498,119		542,548
Collateralized mortgage obligations
AFS investment securities:
Amortized Cost	357,766		829,928
Gross Unrealized Gain	0		0
Gross Unrealized Loss	(30,509)		(65,699)
Estimated Fair Value	327,257		764,229
HTM investment securities:
Amortized Cost	349,328
Allowance for Credit Losses	0
Net Carrying Amount	349,328
Gross Unrecognized Gain	70
Gross Unrecognized Loss	(7,385)
Estimated Fair Value	342,013
Mortgage-backed securities
AFS investment securities:
Amortized Cost	888,740		953,678
Gross Unrealized Gain	0		0
Gross Unrealized Loss	(129,284)		(137,897)
Estimated Fair Value	759,456		815,781
HTM investment securities:
Amortized Cost	224,470		231,692
Allowance for Credit Losses	0		0
Net Carrying Amount	224,470		231,692
Gross Unrecognized Gain	0		0
Gross Unrecognized Loss	(33,460)		(33,621)
Estimated Fair Value	191,010		198,071
Municipal bonds
HTM investment securities:
Amortized Cost	1,147,604		1,148,055
Allowance for Credit Losses	(113)		(43)
Net Carrying Amount	1,147,491		1,148,012
Gross Unrecognized Gain	0		44
Gross Unrecognized Loss	(238,542)		(257,430)
Estimated Fair Value	908,949		890,626
Other
HTM investment securities:
Amortized Cost	16,315		8,399
Allowance for Credit Losses	0		0
Net Carrying Amount	16,315		8,399
Gross Unrecognized Gain	0		0
Gross Unrecognized Loss	0		0
Estimated Fair Value	$ 16,315		$ 8,399