Income Taxes (Effective Income Tax Reconciliation) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
U.S. federal income tax rate									35.00%
Income Tax Expense (Benefit) Reconciliation
Income tax expense at statutory federal income tax rate									$ 135,957	$ 125,501	$ 105,896
State income tax expense, net of federal income tax benefit									13,256	12,870	8,014
Bank-owned life insurance									(3,402)	(2,885)	(2,928)
Change in valuation allowance									(2,055)	(589)	(2,273)
General business tax credits									(1,213)	(1,173)	(1,123)
Tax-exempt income									(825)	(835)	(1,076)
Other, net									(51)	(398)	800
Total income tax expense	$ 39,519	$ 37,375	$ 33,574	$ 31,199	$ 32,342	$ 36,058	$ 32,242	$ 31,849	$ 141,667	$ 132,491	$ 107,310
Effective tax rate									36.50%	36.90%	35.50%