Share-Based Compensation (Details 1) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Time-Based Restricted Stock Units (RSUs) [Member]
Summary of Time-Based RSUs
Outstanding at January 1, 2013, Vested RSUs and Total RSUs	1,048,863
Granted, Shares	157,232
Vested, Shares	0
Settled (in shares)	(8,559)	[1]
Issuance of dividend equivalents	6,864	[2]
Canceled	(3,800)	[1],[3]
Outstanding as of March 31, 2013, Vested RSUs and Total RSUs	1,200,600
Summary of Granted and Vested Time-Based Restricted Stock Units
Granted, Shares	157,232
Vested, Shares	0
Nonvested Restricted Stock Units RSU [Member]
Summary of Time-Based RSUs
Outstanding at January 1, 2013 , Shares	279,102
Outstanding at January 1, 2013, Weighted Average Grant Date Fair Value Per Share	$ 41.30
Granted, Shares	157,232		196,033
Granted, Weighted Average Grant Date Fair Value Per Share	$ 48.88		$ 44.29
Vested, Shares	(64,778)		(48,864)
Vested, Weighted Average Grant Date Fair Value Per Share	$ 37.89
Outstanding as of March 31, 2013, Shares	371,556
Outstanding as of March 31, 2013, Weighted Average Grant Date Fair Value Per Share	$ 45.11
Summary of Granted and Vested Time-Based Restricted Stock Units
Granted, Shares	157,232		196,033
Granted, Weighted Average Grant Date Fair Value Per Share	$ 48.88		$ 44.29
Vested, Shares	(64,778)		(48,864)
Vested shares, total fair value	$ 3,161	[4]	$ 1,961	[4]
Vested Restricted Stock Units RSU [Member]
Summary of Time-Based RSUs
Outstanding at January 1, 2013, Vested RSUs and Total RSUs	769,761
Granted, Shares	0
Vested, Shares	(64,778)
Settled (in shares)	(8,559)
Issuance of dividend equivalents	6,864	[2]
Canceled	(3,800)	[1],[3]
Outstanding as of March 31, 2013, Vested RSUs and Total RSUs	829,044
Summary of Granted and Vested Time-Based Restricted Stock Units
Granted, Shares	0
Vested, Shares	(64,778)

[1] Represents vested RSUs that are settled in cash or shares of the Company's common stock.

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

[3] 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 the issuance, vesting or settlement of RSUs in accordance with the terms of the 2006 Plan.

[4] 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.