Investment Securities - Amortized Cost and Fair Value of Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Available for sale debt securities
Amortized Cost	$ 8,560,733	$ 5,985,031
Unrealized Gains	24,595	97,114
Unrealized Losses	(157,296)	(10,730)
Total available-for-sale securities, Fair value,	8,428,032	6,071,415
Available-for-sale investment securities
Accrued interest receivable related to available-for-sale investment securities	14,100	10,600
Collateralized Loan Obligations [Member]
Available for sale debt securities
Amortized Cost	105,245
Unrealized Gains	2
Total available-for-sale securities, Fair value,	105,247
Residential - Government agency
Available for sale debt securities
Amortized Cost	135,764	155,169
Unrealized Gains	1,791	5,293
Unrealized Losses	(291)
Total available-for-sale securities, Fair value,	137,264	160,462
Residential - Government-sponsored enterprises
Available for sale debt securities
Amortized Cost	1,496,605	434,282
Unrealized Gains	6,914	13,643
Unrealized Losses	(12,419)	(725)
Total available-for-sale securities, Fair value,	1,491,100	447,200
Commercial - Government agency
Available for sale debt securities
Amortized Cost	392,443	583,232
Unrealized Gains	1,741	16,537
Unrealized Losses	(6,521)	(119)
Total available-for-sale securities, Fair value,	387,663	599,650
Commercial - Government-sponsored enterprises
Available for sale debt securities
Amortized Cost	1,415,511	931,095
Unrealized Gains	2,646	9,045
Unrealized Losses	(48,714)	(7,983)
Total available-for-sale securities, Fair value,	1,369,443	932,157
Government agency
Available for sale debt securities
Amortized Cost	2,103,187	1,902,326
Unrealized Gains	7,768	32,246
Unrealized Losses	(31,432)	(1,019)
Total available-for-sale securities, Fair value,	2,079,523	1,933,553
Government-sponsored enterprises
Available for sale debt securities
Amortized Cost	2,671,131	1,808,804
Unrealized Gains	3,608	18,991
Unrealized Losses	(53,695)	(823)
Total available-for-sale securities, Fair value,	2,621,044	1,826,972
Debt securities issued by states and political subdivisions
Available for sale debt securities
Amortized Cost	44,185
Total available-for-sale securities, Fair value,	44,185
U.S. Treasury securities
Available for sale debt securities
Amortized Cost	196,662	170,123
Unrealized Gains	125	1,359
Unrealized Losses	(4,224)	(61)
Total available-for-sale securities, Fair value,	$ 192,563	$ 171,421

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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