Stock-Based Compensation Expense (Summary of Stock-Based Compensation Expense) (Details) (USD $) In Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Stock-based compensation expense	$ 3,026	$ 3,087	$ 5,968	$ 5,829
Stock Options [Member]
Stock-based compensation expense	1,207	1,552	2,500	3,025
Restricted Common Stock [Member]
Stock-based compensation expense	70	548	288	1,114
Restricted Stock Units [Member]
Stock-based compensation expense	1,427	808	2,654	1,473
Performance Stock Units [Member]
Stock-based compensation expense	$ 322	$ 179	$ 526	$ 217