Borrowings - Credit Agreement (Details) - USD ($)	Jan. 29, 2016	Jan. 31, 2014	Jun. 30, 2016	Dec. 31, 2015
Credit Agreement
Amount outstanding under Credit Agreement			$ 10,000,000	$ 0
Interest, fixed rate (as a percent)			2.97%
Term Debt
Term loans			$ 3,438,000	3,606,000
Obligations under capital lease			6,019,000	8,961,000
Total			$ 9,457,000	$ 12,567,000
Revolving Credit Agreement
Credit Agreement
Current borrowing capacity		$ 150,000,000
Credit facility initial term		2 years
New Revolving Credit Agreement
Credit Agreement
Current borrowing capacity	$ 150,000,000
Credit facility initial term	364 days
Maximum borrowing capacity including accordion expansion	$ 225,000,000