Borrowings (Details 2) (USD $)			12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Credit Agreement	Dec. 31, 2012 Credit Agreement Base rate	Dec. 31, 2012 Credit Agreement Federal funds rate	Dec. 31, 2012 Credit Agreement One month Eurodollar London Interbank Offered Rate
Credit Agreement
Current borrowing capacity			$ 150,000,000
Credit facility initial term			3 years
Maximum borrowing capacity including accordion expansion			250,000,000
Interest, base rate				base rate	federal funds rate	one month Eurodollar London Interbank Offered Rate (LIBOR) rate
Interest, margin over base rate (as a percent)			2.50%		2.50%	2.50%
Unused commitment fee (as a percent)			0.50%
Incremental interest rate payable in event of default (as a percent)			2.00%
Term loan	15,388,000
Obligations under capital lease	3,280,000
Interim funding facility under capital lease	604,000
Term debt	$ 19,272,000	$ 23,997,000