Investment Securities - Summary (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Available-for-sale debt securities:
Total	$ 2,814,241	$ 3,598,600
Gross Unrealized Gains	995	9,563
Gross Unrealized Losses	(279,590)	(69,962)
Estimated Fair Value	2,535,646	3,538,201
Held-to-maturity debt securities:
Amortized Cost(1)	980,935	0
Gross Unrealized Gains	0
Gross Unrealized Losses	81,688
Estimated Fair Value	899,247
Equity securities	36,118	45,607
Total investment securities	3,552,699	3,583,808
Interest receivable	57,600	50,900
Available-for-sale
Available-for-sale debt securities:
Total	2,814,241
Estimated Fair Value	2,535,646
Held-to-maturity debt securities:
Interest receivable	5,200	6,600
Held-to-maturity
Held-to-maturity debt securities:
Estimated Fair Value	899,247
Interest receivable	1,600
U.S. Treasury securities
Available-for-sale debt securities:
Total	638,427
Gross Unrealized Gains	974
Gross Unrealized Losses	(13,598)
Estimated Fair Value	625,803
U.S. government agency securities
Available-for-sale debt securities:
Total	125,000	125,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(16,382)	(4,056)
Estimated Fair Value	108,618	120,944
Residential mortgage-backed securities
Available-for-sale debt securities:
Total	2,036,101	3,288,261
Gross Unrealized Gains	21	156
Gross Unrealized Losses	(246,567)	(63,039)
Estimated Fair Value	1,789,555	3,225,378
Held-to-maturity debt securities:
Amortized Cost(1)	980,935
Gross Unrealized Gains	0
Gross Unrealized Losses	81,688
Estimated Fair Value	899,247
Tax-exempt asset-backed securities
Available-for-sale debt securities:
Total		170,626
Gross Unrealized Gains		9,407
Gross Unrealized Losses		0
Estimated Fair Value		180,033
Credit risk transfer (“CRT”) securities
Available-for-sale debt securities:
Total	14,713	14,713
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(3,043)	(2,867)
Estimated Fair Value	$ 11,670	$ 11,846

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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