Revolving Credit Facility and Long-Term Debt - Principal Balances under Long-term Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Sep. 03, 2018	Dec. 31, 2017
Line of Credit Facility [Line Items]
Total long-term debt	$ 395,152		$ 278,472
Collateralized debt facility	7,000	$ 7,000	6,959
Less unamortized debt issuance costs	(348)		(487)
Less current portion	22,000		19,459
Long-term portion	373,152		259,013
Term Loan
Line of Credit Facility [Line Items]
Total long-term debt	72,500		85,000
Revolving Credit Facility
Line of Credit Facility [Line Items]
Total long-term debt	$ 316,000		$ 187,000