Share-Based Compensation (Details 1) (USD $) In Thousands, except Share data	9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010
Restricted Stock Units (RSUs) [Member]
Summary of restricted stock units
Outstanding at January 1, 2011, Vested RSUs and Total RSUs	713,822
Granted, Non-Vested Shares	107,673
Issuance of dividend equivalents	20,790	[1]
Cancelled	(8,497)	[2]
Outstanding as of September 30, 2011,Vested RSUs and Total RSUs	833,788
Summary of Granted and Vested Restricted Stock Units
Granted, Non-Vested Shares	107,673
Nonvested Restricted Stock Units RSU [Member]
Summary of restricted stock units
Outstanding at January 1, 2011 , Shares	125,754
Outstanding at January 1, 2011, Weighted Average Grant Date Fair Value Per Share	$ 29.88
Granted, Non-Vested Shares	107,673		159,606
Granted, Weighted Average Grant Date Fair Value Per Share	$ 37.94		$ 30.24
Vested, Shares	(23,035)		(23,564)
Vested, Weighted Average Grant Date Fair Value Per Share	$ 30.57
Outstanding as of September 30, 2011, Shares	210,392
Outstanding as of September 30, 2011, Weighted Average Grant Date Fair Value Per Share	$ 33.93
Summary of Granted and Vested Restricted Stock Units
Granted, Non-Vested Shares	107,673		159,606
Granted, Weighted Average Grant Date Fair Value Per Share	$ 37.94		$ 30.24
Vested, Shares	(23,035)		(23,564)
Vested shares, total fair value	$ 897	[3]	$ 740	[3]
Vested Restricted Stock Units R S U [Member]
Summary of restricted stock units
Outstanding at January 1, 2011, Vested RSUs and Total RSUs	588,068
Granted, Non-Vested Shares	0
Vested, Shares	(23,035)
Issuance of dividend equivalents	20,790	[1]
Cancelled	(8,497)	[2]
Outstanding as of September 30, 2011,Vested RSUs and Total RSUs	623,396
Summary of Granted and Vested Restricted Stock Units
Granted, Non-Vested Shares	0
Vested, Shares	(23,035)

[1] RSUs issued as dividend equivalents are vested upon issuance.

[2] We accept the return of RSUs, at the current quoted closing share price of the Company's common stock, to satisfy minimum statutory tax-withholding requirements related to either RSUs that have vested or RSU dividend equivalents in accordance with the terms of the 2006 Plan.

[3] Total fair value of RSUs vested was calculated based on the quoted closing share price of the Company's common stock on the NYSE on the day of vesting.