Federal and State Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets [Abstract]
Credit loss reserves	$ 101,265	$ 50,611
Lease liability	44,794	46,084
Deferred compensation	29,504	25,976
Unearned fees	14,584	9,080
Purchased loan discount	11,537	18,042
Share-based compensation	6,525	7,392
Valuation adjustments	3,834	1,545
Other	29,963	26,384
Total deferred tax assets	242,006	185,114
Valuation Allowance [Abstract]
Valuation allowance	0	0
Deferred tax liabilities [Abstract]
Available for sale securities mark to market	105,769	33,140
Right-of-use asset	38,635	42,180
Mortgage servicing rights	24,182	48,435
Acquired identifiable intangible	18,138	23,181
Depreciation	13,754	18,909
Lease financing	11,828	10,720
Other	39,210	34,826
Total deferred tax liabilities	251,516	211,391
Deferred Tax Liabilities, Net	(9,510)	(26,277)
Current income tax expense [Abstract]
Federal	173,888	110,887	$ 103,748
State	29,889	15,088	15,253
Total current income tax expense	203,777	125,975	119,001
Deferred income tax expense [Abstract]
Federal	(65,989)	3,416	(190)
State	(8,995)	792	250
Total deferred income tax expense (benefit)	(74,984)	4,208	60
Total income tax expense	128,793	130,183	119,061
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Federal statutory tax	118,412	132,482	118,752
Tax exempt revenue	(7,035)	(12,227)	(8,311)
Effect of state income taxes, net of federal benefit	14,251	12,715	12,430
Utilization of tax credits, net of proportional amortization of low-income housing limited partnership investments	(6,994)	(5,127)	(4,559)
Other, net	10,159	2,340	749
Total income tax expense	$ 128,793	$ 130,183	$ 119,061
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal statutory tax (in thousandths)	21.00%	21.00%	21.00%
Tax exempt revenue (in thousandths)	(1.20%)	(1.90%)	(1.50%)
Effect of state income taxes, net of federal benefit (in thousandths)	2.50%	2.00%	2.20%
Utilization of tax credits, net of proportional amortization of low-income housing limited partnership investments (in thousandths)	(1.20%)	(0.80%)	(0.80%)
Other, net (in thousandths)	1.70%	0.30%	0.20%
Total (in thousandths)	22.80%	20.60%	21.10%
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance as of January 1	$ 20,465	$ 18,869	$ 18,110
Additions for tax for current year positions	6,384	5,649	2,649
Settlements during the period	0	0	0
Lapses of applicable statute of limitations	(3,947)	(4,053)	(1,890)
Balance as of December 31	22,902	20,465	18,869
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	17,200
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	2,400	2,200	$ 1,700
Unrecognized Tax Benefits, Penalties and Interest Accrued	$ 5,900	$ 5,600
Unrecognized Tax Benefits, Number of Reporting Periods Open for Examination, Federal	3
Unrecognized Tax Benefits, Number of Reporting Periods Open for Examination, State, Minimum	3
Unrecognized Tax Benefits, Number of Reporting Periods Open for Examination, State, Maximum	6