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Investment Securities - Amortized Cost and Estimated Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022	Dec. 31, 2021
AFS investment securities:
Amortized Cost	$ 2,365,873	$ 2,904,745
Gross Unrealized Gain	0	0
Gross Unrealized Loss	(253,021)	(303,732)
Estimated Fair Value	2,112,852	2,601,013
HTM investment securities:
Amortized Cost	1,749,257	1,388,146
Allowance for Credit Losses	(227)	(43)	$ (41)	$ (22)
Net Carrying Amount	1,749,030	1,388,103
Gross Unrecognized Gain	1,596	44
Gross Unrecognized Loss	(254,132)	(291,051)
Estimated Fair Value	1,496,494	1,097,096
U.S. Treasury
AFS investment securities:
Amortized Cost	14,941	49,156
Gross Unrealized Gain	0	0
Gross Unrealized Loss	(1,586)	(2,139)
Estimated Fair Value	13,355	47,017
Agency
AFS investment securities:
Amortized Cost	464,491	485,331
Gross Unrealized Gain	0	0
Gross Unrealized Loss	(46,760)	(53,893)
Estimated Fair Value	417,731	431,438
Corporate
AFS investment securities:
Amortized Cost	561,380	586,652
Gross Unrealized Gain	0	0
Gross Unrealized Loss	(53,191)	(44,104)
Estimated Fair Value	508,189	542,548
Collateralized mortgage obligations
AFS investment securities:
Amortized Cost	401,105	829,928
Gross Unrealized Gain	0	0
Gross Unrealized Loss	(28,473)	(65,699)
Estimated Fair Value	372,632	764,229
HTM investment securities:
Amortized Cost	356,435
Allowance for Credit Losses	0
Net Carrying Amount	356,435
Gross Unrecognized Gain	1,198
Gross Unrecognized Loss	(481)
Estimated Fair Value	357,152
Mortgage-backed securities
AFS investment securities:
Amortized Cost	923,956	953,678
Gross Unrealized Gain	0	0
Gross Unrealized Loss	(123,011)	(137,897)
Estimated Fair Value	800,945	815,781
HTM investment securities:
Amortized Cost	228,624	231,692
Allowance for Credit Losses	0	0
Net Carrying Amount	228,624	231,692
Gross Unrecognized Gain	0	0
Gross Unrecognized Loss	(30,621)	(33,621)
Estimated Fair Value	198,003	198,071
Municipal bonds
HTM investment securities:
Amortized Cost	1,147,822	1,148,055
Allowance for Credit Losses	(227)	(43)
Net Carrying Amount	1,147,595	1,148,012
Gross Unrecognized Gain	398	44
Gross Unrecognized Loss	(223,030)	(257,430)
Estimated Fair Value	924,963	890,626
Other
HTM investment securities:
Amortized Cost	16,376	8,399
Allowance for Credit Losses	0	0
Net Carrying Amount	16,376	8,399
Gross Unrecognized Gain	0	0
Gross Unrecognized Loss	0	0
Estimated Fair Value	$ 16,376	$ 8,399