Borrowings (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2011
Borrowings
Term loan	$ 21,755,000
Obligations under capital lease	2,242,000
Term debt	23,997,000
Credit Agreement
Interest, base rate	three-month LIBOR rate for dollar deposits
Credit Agreement
Credit Agreement
Current borrowing capacity	150,000,000
Credit facility initial term (in years)	3
Maximum borrowing capacity including accordion expansion	$ 250,000,000
Interest, base rate	the higher of the (1) federal funds rate or (2) the one month Eurodollar London Interbank Offered Rate (LIBOR) rate
Interest, margin over base rate (as a percent)	2.50%
Unused commitment fee (as a percent)	0.50%
Incremental interest rate payable in event of default (as a percent)	2.00%