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Investment Securities - Summary of Investment Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Jun. 30, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020
Held-to-maturity
Amortized Cost	$ 3,788,460		$ 1,530,500
Allowance for credit losses on HTM	(1,384)	$ (1,381)	(1,279)	$ (1,279)	$ (1,132)	$ (2,915)
Net Carrying Amount	3,787,076		1,529,221
Gross Unrealized Gains	1,129		6,398
Gross Unrealized (Losses)	(804,165)		(18,241)
Estimated Fair Value	2,984,040		1,517,378
Available-for-sale
Amortized Cost	4,484,131		7,130,861
Allowance for Credit Losses	0		0	0		(312)
Gross Unrealized Gains	395		44,005
Gross Unrealized (Losses)	(546,983)		(61,321)
Estimated Fair Value	3,937,543		7,113,545
U.S. Treasury
Available-for-sale
Amortized Cost	2,250		300
Allowance for Credit Losses	0		0
Gross Unrealized Gains	0		0
Gross Unrealized (Losses)	(59)		0
Estimated Fair Value	2,191		300
U.S. Government agencies
Held-to-maturity
Amortized Cost	447,400		232,609
Allowance for credit losses on HTM	0		0
Net Carrying Amount	447,400		232,609
Gross Unrealized Gains	0		0
Gross Unrealized (Losses)	(97,871)		(7,914)
Estimated Fair Value	349,529		224,695
Available-for-sale
Amortized Cost	195,369		374,754
Allowance for Credit Losses	0		0
Gross Unrealized Gains	145		495
Gross Unrealized (Losses)	(7,454)		(10,608)
Estimated Fair Value	188,060		364,641
Mortgage-backed securities
Held-to-maturity
Amortized Cost	1,214,882		70,342
Allowance for credit losses on HTM	0		0
Net Carrying Amount	1,214,882		70,342
Gross Unrealized Gains	1,069		232
Gross Unrealized (Losses)	(131,437)		(1,425)
Estimated Fair Value	1,084,514		69,149
Available-for-sale
Amortized Cost	2,959,882		4,485,548
Allowance for Credit Losses	0		0
Gross Unrealized Gains	5		6,307
Gross Unrealized (Losses)	(289,539)		(43,239)
Estimated Fair Value	2,670,348		4,448,616
State and political subdivisions
Held-to-maturity
Amortized Cost	1,865,310		1,210,248
Allowance for credit losses on HTM	(107)	(103)	(1,197)	(1,196)	(871)	(2,307)
Net Carrying Amount	1,865,203		1,209,051
Gross Unrealized Gains	60		6,166
Gross Unrealized (Losses)	(540,980)		(8,462)
Estimated Fair Value	1,324,283		1,206,755
Available-for-sale
Amortized Cost	1,054,356		1,791,097
Allowance for Credit Losses	0		0	0		(217)
Gross Unrealized Gains	244		30,556
Gross Unrealized (Losses)	(232,091)		(1,995)
Estimated Fair Value	822,509		1,819,658
Other securities
Held-to-maturity
Amortized Cost	260,868		17,301
Allowance for credit losses on HTM	(1,277)	$ (1,278)	(82)	(83)	$ (261)	(608)
Net Carrying Amount	259,591		17,219
Gross Unrealized Gains	0		0
Gross Unrealized (Losses)	(33,877)		(440)
Estimated Fair Value	225,714		16,779
Available-for-sale
Amortized Cost	272,274		479,162
Allowance for Credit Losses	0		0	$ 0		$ (95)
Gross Unrealized Gains	1		6,647
Gross Unrealized (Losses)	(17,840)		(5,479)
Estimated Fair Value	$ 254,435		$ 480,330