Stockholder's Equity (Details Textual) (USD $)	1 Months Ended	9 Months Ended
	Oct. 31, 2010	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Stockholder's Equity (Additional Textual) [Abstract]
Common Stock Reserved and Available For Issuance		1,500,000
Percentage of directors' stock grant vested on one year anniversary date		100.00%
Weighted average grant date fair value of nonvested shares granted during period		$ 19.02
Total unrecognized compensation cost related to nonvested shares of common stock granted		$ 8,900,000
Weighted average period of Cost Recognized		3 years 2 months 12 days
Total fair Value of Shares of common stock vested		3,500,000	3,500,000
Compensation expense related to nonvested stock grants		3,400,000	3,000,000
Price of shares issued under Employee Stock Purchase Plan as a percentage of FMV		95.00%
Number of shares reserved for the Employee Stock Purchase Plan		250,000
Options Issued and Exercisable		15,000
Options Forfeited		0
Options Exercised		0
Options Granted		0
Shares redeemed to satisfy personal tax obligations.		32,756
Value of shares redeemed to satisfy personal tax obligations		602,000
Par value of common stock repurchased	$ 0.01	$ 0.01		$ 0.01
Total amount authorized for repurchase under Company's Stock Repurchase Program	50,000,000
Number of shares of common stock repurchased during period		1,093,659
Repurchase of common stock, value		(19,017,000)
Average cost per share of common stock repurchased during period		$ 17.39
Remaining amount authorized for repurchase under Company's Stock Repurchase Program		30,400,000
Amount received for sale of membership interests		80,000
Percentage of membership interests sold		40.00%
Change in Additional Paid in Capital as a result of the sale of membership interests		80,000
Total purchase price for additional membership interests purchased		126,000
Reduction in noncontrolling interest redeemable as a result of the purchase of membership interests		(88,000)
Change in Additional Paid in Capital as a result of the purchase of membership interests		$ 38,000
Director [Member]
Stockholder's Equity (Textual) [Abstract]
Nonvested stock grants to independent directors		26,100
Director Period of Vested Shares		1 year
Employee [Member]
Stockholder's Equity (Textual) [Abstract]
Nonvested stock grants to employees		187,140
Period of Vested Shares		5 years