Revolving Credit Facility and Long-Term Debt - Principal Balances under Long-term Debt (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Total long-term debt	$ 400,221	$ 395,152
Collateralized debt facility	0	7,000
Less unamortized debt issuance costs	(279)	(348)
Less current portion	15,000	22,000
Long-term portion	385,221	373,152
Term Loan
Line of Credit Facility [Line Items]
Total long-term debt	65,000	72,500
Revolving Credit Facility
Line of Credit Facility [Line Items]
Total long-term debt	$ 335,500	$ 316,000