Investment Securities - Summary of Investment Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021
Held-to-maturity
Amortized Cost	$ 3,759,968		$ 3,761,094
Allowance for credit losses on HTM	(3,214)	$ (1,888)	(1,388)	$ (1,381)	$ (1,377)	$ (1,279)
Net Carrying Amount	3,756,754		3,759,706
Gross Unrealized Gains	67		283
Gross Unrealized (Losses)	(661,963)		(696,756)
Estimated Fair Value	3,094,858		3,063,233
Available-for-sale
Amortized Cost	4,012,265		4,331,413
Allowance for Credit Losses	(2,396)	(5,800)	0
Gross Unrealized Gains	239		373
Gross Unrealized (Losses)	(430,350)		(478,932)
Estimated Fair Value	3,579,758		3,852,854
U.S. Government agencies
Held-to-maturity
Amortized Cost	451,737		448,012
Allowance for credit losses on HTM	0		0
Net Carrying Amount	451,737		448,012
Gross Unrealized Gains	0		0
Gross Unrealized (Losses)	(94,515)		(102,558)
Estimated Fair Value	357,222		345,454
Available-for-sale
Amortized Cost	183,735		191,498
Allowance for Credit Losses	0		0
Gross Unrealized Gains	51		103
Gross Unrealized (Losses)	(7,222)		(7,322)
Estimated Fair Value	176,564		184,279
U.S. Treasury
Available-for-sale
Amortized Cost	2,271		2,257
Allowance for Credit Losses	0		0
Gross Unrealized Gains	0		0
Gross Unrealized (Losses)	(62)		(60)
Estimated Fair Value	2,209		2,197
Mortgage-backed securities
Held-to-maturity
Amortized Cost	1,193,118		1,190,781
Allowance for credit losses on HTM	0		0
Net Carrying Amount	1,193,118		1,190,781
Gross Unrealized Gains	0		227
Gross Unrealized (Losses)	(118,728)		(118,960)
Estimated Fair Value	1,074,390		1,072,048
Available-for-sale
Amortized Cost	2,532,234		2,809,319
Allowance for Credit Losses	0		0
Gross Unrealized Gains	4		20
Gross Unrealized (Losses)	(249,910)		(266,437)
Estimated Fair Value	2,282,328		2,542,902
State and political subdivisions
Held-to-maturity
Amortized Cost	1,859,956		1,861,102
Allowance for credit losses on HTM	(934)	(362)	(110)	(103)	(1,285)	(1,197)
Net Carrying Amount	1,859,022		1,860,992
Gross Unrealized Gains	67		56
Gross Unrealized (Losses)	(415,230)		(446,198)
Estimated Fair Value	1,443,859		1,414,850
Available-for-sale
Amortized Cost	1,029,164		1,056,124
Allowance for Credit Losses	0	0	0
Gross Unrealized Gains	184		250
Gross Unrealized (Losses)	(143,843)		(185,300)
Estimated Fair Value	885,505		871,074
Other securities
Held-to-maturity
Amortized Cost	255,157		261,199
Allowance for credit losses on HTM	(2,280)	(1,526)	(1,278)	$ (1,278)	$ (92)	$ (82)
Net Carrying Amount	252,877		259,921
Gross Unrealized Gains	0		0
Gross Unrealized (Losses)	(33,490)		(29,040)
Estimated Fair Value	219,387		230,881
Available-for-sale
Amortized Cost	264,861		272,215
Allowance for Credit Losses	(2,396)	$ (5,800)	0
Gross Unrealized Gains	0		0
Gross Unrealized (Losses)	(29,313)		(19,813)
Estimated Fair Value	$ 233,152		$ 252,402