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, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014 Rate	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Income tax expense based upon the Federal statutory rate on income before income taxes									$ 86,251	$ 78,554	$ 63,046
Increase (decrease) in tax resulting from:
Tax-exempt interest, net of interest expense disallowance									(1,936)	(1,423)	(1,294)
State taxes, net of federal tax benefit									10,731	10,355	7,811
Income earned on bank owned life insurance									(896)	(1,157)	(974)
Non-deductible compensation costs									561	654	1,156
Meals, entertainment and related expenses									1,026	993	931
Foreign subsidiary, net									775	588	1,991
Foreign tax credits									0	0	(2,177)
Tax credits, excluding foreign tax credits									(1,498)	(1,553)	(1,906)
Other, net									19	219	352
Total income tax expense	$ 23,669	$ 25,034	$ 24,490	$ 21,840	$ 22,534	$ 22,519	$ 21,943	$ 20,234	$ 95,033	$ 87,230	$ 68,936
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent									35.00%