Investment Securities - Amortized Cost and Estimated Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
AFS investment securities:
Amortized Cost	$ 2,908,511	$ 4,278,589
Gross Unrealized Gain	98	46,232
Gross Unrealized Loss	(229,539)	(50,957)
Estimated Fair Value	2,679,070	4,273,864
HTM investment securities:
Amortized Cost	1,390,791	381,696
Allowance for Credit Losses	(109)	(22)
Net Carrying Amount	1,390,682	381,674
Gross Unrecognized Gain	457	4,398
Gross Unrecognized Loss	(234,638)	(1,649)
Estimated Fair Value	1,156,501	384,423
U.S. Treasury
AFS investment securities:
Amortized Cost	34,750	57,708
Gross Unrealized Gain	0	614
Gross Unrealized Loss	(1,390)	(456)
Estimated Fair Value	33,360	57,866
Agency
AFS investment securities:
Amortized Cost	452,845	440,183
Gross Unrealized Gain	34	2,081
Gross Unrealized Loss	(40,584)	(10,129)
Estimated Fair Value	412,295	432,135
Corporate debt
AFS investment securities:
Amortized Cost	602,320	451,621
Gross Unrealized Gain	36	6,096
Gross Unrealized Loss	(32,941)	(3,856)
Estimated Fair Value	569,415	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	1,148,411	368,344
Allowance for Credit Losses	(109)	(22)
Net Carrying Amount	1,148,302	368,322
Gross Unrecognized Gain	448	3,834
Gross Unrecognized Loss	(211,542)	(1,649)
Estimated Fair Value	937,208	370,507
Collateralized mortgage obligations
AFS investment securities:
Amortized Cost	832,341	680,686
Gross Unrealized Gain	28	2,012
Gross Unrealized Loss	(42,583)	(6,055)
Estimated Fair Value	789,786	676,643
Mortgage-backed securities
AFS investment securities:
Amortized Cost	986,255	1,586,406
Gross Unrealized Gain	0	3,220
Gross Unrealized Loss	(112,041)	(26,180)
Estimated Fair Value	874,214	1,563,446
HTM investment securities:
Amortized Cost	240,918	11,843
Allowance for Credit Losses	0	0
Net Carrying Amount	240,918	11,843
Gross Unrecognized Gain	9	564
Gross Unrecognized Loss	(23,096)	0
Estimated Fair Value	217,831	12,407
Other
HTM investment securities:
Amortized Cost	1,462	1,509
Allowance for Credit Losses	0	0
Net Carrying Amount	1,462	1,509
Gross Unrecognized Gain	0	0
Gross Unrecognized Loss	0	0
Estimated Fair Value	$ 1,462	$ 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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