Revolving Credit Facility and Long-Term Debt - Principal Balances under Long-term Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Feb. 23, 2017	Dec. 31, 2016
Line of Credit Facility [Line Items]
Total long-term debt	$ 278,472		$ 324,373
2017 Debt facility	6,959	$ 7,000	0
Less unamortized debt issuance costs	(487)		(627)
Less current portion	19,459		10,000
Long-term portion	259,013		314,373
Term Loan
Line of Credit Facility [Line Items]
Total long-term debt	85,000		145,000
Revolving Credit Facility
Line of Credit Facility [Line Items]
Total long-term debt	$ 187,000		$ 180,000