Income Taxes (Reconciliation of the Differences Between Taxes Computed Using the Statutory Federal Income Tax Rate and Actual Income Tax Expense) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Income tax expense based upon the Federal statutory rate on income before income taxes									$ 88,118	$ 86,251	$ 78,554
Increase (decrease) in tax resulting from:
Tax-exempt interest, net of interest expense disallowance									(2,878)	(1,936)	(1,423)
State taxes, net of federal tax benefit									9,996	10,731	10,355
Income earned on bank owned life insurance									(1,562)	(896)	(1,157)
Non-deductible compensation costs									528	561	654
Meals, entertainment and related expenses									1,283	1,026	993
Foreign subsidiary, net									148	775	588
Tax benefits related to tax credit investments									(778)	(1,498)	(1,553)
Other, net									161	19	219
Total income tax expense	$ 20,896	$ 23,842	$ 26,295	$ 23,983	$ 23,669	$ 25,034	$ 24,490	$ 21,840	$ 95,016	$ 95,033	$ 87,230
Effective income tax rate reconciliation, at Federal satutory income tax rate, percent									35.00%