Parent Company (Details 1) (USD $) In Thousands, unless otherwise specified	3 Months Ended															12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2010		Sep. 30, 2010		Jun. 30, 2010		Mar. 31, 2010		Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Condensed Financial Statements, Captions [Line Items]
Income before income tax expense																$ 165,651	$ 140,000	$ 107,815
Income tax benefit																(46,093)	(37,091)	(25,645)
Net income	30,496	31,737	[1]	29,763	[1]	27,560	[1]	27,030	[1]	28,996	[1]	31,493	[1]	15,390	[1]	119,558	102,909	82,170
Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Cash dividends from subsidiaries																72,500	22,720	31,125
Other income																287	1,502	2,881
Total Income																72,787	24,222	34,006
Interest and other expenses																8,005	10,387	12,065
Income before income tax expense																64,782	13,835	21,941
Income tax benefit																(1,803)	(2,267)	(3,336)
Income before undistributed income of subsidiaries																66,585	16,102	25,277
Equity in undistributed income of subsidiaries																52,973	86,807	56,893
Net income																$ 119,558	$ 102,909	$ 82,170

[1] * Net income restated to reflect purchase accounting adjustments which decreased the bargain purchase gain recognized on the George Washington acquisition to $1.0 million in the quarter ended March 31, 2010.