Investment Securities - Amortized Cost and Fair Value of Available-for-Sale Investment Securities Portfolio (Details) - USD ($)	Jun. 30, 2022	Dec. 31, 2021
Available-for-Sale
Amortized Cost	$ 8,250,226,000	$ 7,384,033,000
Unrealized Gains	5,112,000	112,282,000
Unrealized Losses	(579,833,000)	(118,235,000)
Basis adjustments	(107,804,000)	3,986,000
Fair Value	7,567,701,000	7,382,066,000
Held-to-Maturity
Amortized Cost	3,084,186,000	0
Unrealized Gains	239,000
Unrealized Losses	(305,135,000)
Basis adjustments	0
Allowance for securities held-to-maturity	(151,000)
Fair Value	2,779,290,000	0
Total held-to-maturity securities	3,084,186,000	0
U.S. Treasury
Available-for-Sale
Amortized Cost	441,846,000	234,555,000
Unrealized Gains	9,000	1,233,000
Unrealized Losses	(7,739,000)	(7,751,000)
Basis adjustments	(31,333,000)	7,547,000
Fair Value	402,783,000	235,584,000
U.S. government-sponsored entities and agencies
Available-for-Sale
Amortized Cost	1,442,261,000	1,575,994,000
Unrealized Gains	1,000	7,354,000
Unrealized Losses	(123,234,000)	(37,014,000)
Basis adjustments	(76,471,000)	(3,561,000)
Fair Value	1,242,557,000	1,542,773,000
Held-to-Maturity
Amortized Cost	815,833,000
Unrealized Gains	0
Unrealized Losses	(95,398,000)
Basis adjustments	0
Fair Value	720,435,000
Mortgage-backed securities
Available-for-Sale
Amortized Cost	5,227,908,000	3,737,484,000
Unrealized Gains	794,000	27,421,000
Unrealized Losses	(400,994,000)	(66,074,000)
Basis adjustments	0	0
Fair Value	4,827,708,000	3,698,831,000
Held-to-Maturity
Amortized Cost	1,149,212,000
Unrealized Gains	170,000
Unrealized Losses	(59,940,000)
Basis adjustments	0
Fair Value	1,089,442,000
States and political subdivisions
Available-for-Sale
Amortized Cost	740,026,000	1,587,172,000
Unrealized Gains	4,132,000	69,696,000
Unrealized Losses	(24,117,000)	(1,882,000)
Basis adjustments	0	0
Fair Value	720,041,000	1,654,986,000
Held-to-Maturity
Amortized Cost	1,119,292,000
Unrealized Gains	69,000
Unrealized Losses	(149,797,000)
Basis adjustments	0
Fair Value	969,564,000
Pooled trust preferred securities
Available-for-Sale
Amortized Cost	13,768,000	13,756,000
Unrealized Gains	0	0
Unrealized Losses	(2,667,000)	(4,260,000)
Basis adjustments	0	0
Fair Value	11,101,000	9,496,000
Other securities
Available-for-Sale
Amortized Cost	384,417,000	235,072,000
Unrealized Gains	176,000	6,578,000
Unrealized Losses	(21,082,000)	(1,254,000)
Basis adjustments	0	0
Fair Value	$ 363,511,000	$ 240,396,000