Investment Securities - Amortized Cost and Estimated Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
AFS investment securities:
Amortized Cost	$ 2,985,391	$ 4,278,589
Gross Unrealized Gain	24	46,232
Gross Unrealized Loss	(324,336)	(50,957)
Estimated Fair Value	2,661,079	4,273,864
HTM investment securities:
Amortized Cost	1,385,593	381,696
Allowance for Credit Losses	(91)	(22)
Net Carrying Amount	1,385,502	381,674
Gross Unrecognized Gain	0	4,398
Gross Unrecognized Loss	(330,315)	(1,649)
Estimated Fair Value	1,055,187	384,423
U.S. Treasury
AFS investment securities:
Amortized Cost	48,926	57,708
Gross Unrealized Gain	0	614
Gross Unrealized Loss	(2,152)	(456)
Estimated Fair Value	46,774	57,866
Agency
AFS investment securities:
Amortized Cost	486,111	440,183
Gross Unrealized Gain	0	2,081
Gross Unrealized Loss	(55,248)	(10,129)
Estimated Fair Value	430,863	432,135
Corporate debt
AFS investment securities:
Amortized Cost	602,058	451,621
Gross Unrealized Gain	0	6,096
Gross Unrealized Loss	(46,308)	(3,856)
Estimated Fair Value	555,750	453,861
Municipal bonds
AFS investment securities:
Amortized Cost		1,061,985
Gross Unrealized Gain		32,209
Gross Unrealized Loss		(4,281)
Estimated Fair Value		1,089,913
HTM investment securities:
Amortized Cost	1,148,234	368,344
Allowance for Credit Losses	(91)	(22)
Net Carrying Amount	1,148,143	368,322
Gross Unrecognized Gain	0	3,834
Gross Unrecognized Loss	(294,439)	(1,649)
Estimated Fair Value	853,704	370,507
Collateralized mortgage obligations
AFS investment securities:
Amortized Cost	856,867	680,686
Gross Unrealized Gain	24	2,012
Gross Unrealized Loss	(65,776)	(6,055)
Estimated Fair Value	791,115	676,643
Mortgage-backed securities
AFS investment securities:
Amortized Cost	991,429	1,586,406
Gross Unrealized Gain	0	3,220
Gross Unrealized Loss	(154,852)	(26,180)
Estimated Fair Value	836,577	1,563,446
HTM investment securities:
Amortized Cost	235,937	11,843
Allowance for Credit Losses	0	0
Net Carrying Amount	235,937	11,843
Gross Unrecognized Gain	0	564
Gross Unrecognized Loss	(35,876)	0
Estimated Fair Value	200,061	12,407
Other
HTM investment securities:
Amortized Cost	1,422	1,509
Allowance for Credit Losses	0	0
Net Carrying Amount	1,422	1,509
Gross Unrecognized Gain	0	0
Gross Unrecognized Loss	0	0
Estimated Fair Value	$ 1,422	$ 1,509

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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