Employee Benefit Plan (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Employee Benefit Plan [Abstract]
Maximum limit on pretax deferral contribution by eligible employees	50.00%
Total contribution made by employer under matching program	$ 1,362,000	$ 822,000	$ 798,000