Federal and State Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets [Abstract]
Available for sale securities mark to market	$ 5,779	$ 0
Share-based compensation	9,360	10,522
Credit loss allowances	99,191	88,906
Valuation adjustments	12,222	6,957
Deferred compensation	30,262	25,950
Unearned fees	11,877	11,124
Other	42,541	34,169
Total deferred tax assets	211,232	177,628
Valuation Allowance [Abstract]
Valuation allowance	0	0
Deferred tax liabilities [Abstract]
Available for sale securities mark to market	0	14,828
Depreciation	25,877	22,080
Mortgage servicing rights	92,748	77,900
Lease financing	17,923	22,301
Other	45,363	41,904
Total deferred tax liabilities	181,911	179,013
Net deferred tax assets	29,321
Net deferred tax liabilities		(1,385)
Current income tax expense [Abstract]
Federal	107,379	117,566	$ 95,289
State	11,028	12,397	9,392
Total current income tax expense	118,407	129,963	104,681
Deferred income tax expense [Abstract]
Federal	(11,340)	8,397	36,521
State	(690)	1,024	2,949
Total deferred income tax expense	(12,030)	9,421	39,470
Total income tax expense	106,377	139,384	144,151
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Federal statutory tax	118,530	151,075	153,870
Tax exempt revenue	(10,544)	(9,553)	(8,446)
Effect of state income taxes, net of federal benefit	6,478	9,082	9,054
Utilization of tax credits: [Abstract]
Low-income housing tax credits, net of amortization	(4,171)	(3,874)	(2,953)
Other tax credits	(2,085)	(2,085)	(2,109)
Bank-owned life insurance	(2,911)	(3,264)	(3,183)
Other, net	1,080	(1,997)	(2,082)
Total income tax expense	$ 106,377	$ 139,384	$ 144,151
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal statutory tax (in hundredths)	35.00%	35.00%	35.00%
Tax exempt revenue (in hundredths)	(3.10%)	(2.20%)	(1.90%)
Effect of state income taxes, net of federal benefit (in hundredths)	1.90%	2.10%	2.10%
Utilization of tax credits: [Abstract]
Low-income housing tax credits, net of amortization (in hundredths)	(1.20%)	(0.90%)	(0.70%)
Other tax credits (in hundredths)	(0.60%)	(0.50%)	(0.50%)
Bank-owned life insurance (in hundredths)	(0.90%)	(0.70%)	(0.70%)
Other, net (in hundredths)	0.30%	(0.50%)	(0.50%)
Total (in hundredths)	31.40%	32.30%	32.80%
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance as of January 1	$ 13,232	$ 13,374	$ 12,058
Additions for tax for current year positions	5,640	2,226	3,813
Settlements during the period	0	0	0
Lapses of applicable statute of limitations	(3,031)	(2,368)	(2,497)
Balance as of December 31	15,841	13,232	13,374
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	10,300
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	1,000	1,000	$ 1,500
Unrecognized Tax Benefits, Penalties and Interest Accrued	$ 3,500	$ 3,300
Unrecognized Tax Benefits, Number of Reporting Periods Open for Examination, Federal	3 years
Unrecognized Tax Benefits, Number of Reporting Periods Open for Examination, State, Minimum	3 years
Unrecognized Tax Benefits, Number of Reporting Periods Open for Examination, State, Maximum	6 years