Borrowings - Credit Agreement (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Credit Agreement
Term loans	$ 3,606	$ 2,653
Obligations under capital lease	8,961	15,128
Total	$ 12,567	$ 17,781
New Credit Agreement | Federal funds rate
Credit Agreement
Interest, margin over base rate (as a percent)	2.50%
New Revolving Credit Agreement
Credit Agreement
Current borrowing capacity	$ 150,000
Credit facility initial term	2 years
Unused commitment fee (as a percent)	0.50%
Incremental interest rate payable in event of default (as a percent)	2.00%
Amount outstanding under Credit Agreement	$ 0
New Revolving Credit Agreement | Base rate
Credit Agreement
Interest, base rate	base rate
New Revolving Credit Agreement | One month Eurodollar London Interbank Offered Rate
Credit Agreement
Interest, margin over base rate (as a percent)	2.50%