Available-For-Sale Securities (Narrative) (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2012 bonds securities	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012 bonds securities	Dec. 31, 2011	Dec. 31, 2010
Schedule of Available-for-sale Securities [Line Items]
Number of bonds in a continuous unrealized loss position, twelve months or longer	9								9
Number of trust preferred securities in a continuous unrealized loss position, twelve months or longer	3								3
Income tax expense	$ 18,782,000	$ 19,871,000	$ 15,734,000	$ 14,549,000	$ 12,753,000	$ 19,844,000	$ 7,215,000	$ 10,646,000	$ 68,936,000	$ 50,458,000	$ 37,478,000
Securities, carrying value	1,100,000,000				1,100,000,000				1,100,000,000	1,100,000,000
U.S. Government-sponsored agency securities, to include shareholders equity	10.00%								10.00%
Available-for-sale Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Income tax expense									$ 1,900,000	$ 705,000	$ 3,800,000