Share-based Compensation (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Share-Based Compensation
Share-based compensation expense	$ 5,992	$ 4,904
Stock options
Share-Based Compensation
Vesting period	4 years
Share-based compensation expense	4,520	3,882
Performance shares
Share-Based Compensation
Vesting period	3 years
Share-based compensation expense	1,195	790
Restricted shares
Share-Based Compensation
Vesting period	1 year
Share-based compensation expense	231	181
Employee Stock Purchase Plan
Share-Based Compensation
Share-based compensation expense	$ 46	$ 51