Revolving Credit Facility and Long-Term Debt - Principal Balances under Long-term Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Long-term debt	$ 440,500
Collateralized debt facility		$ 7,000
Less unamortized debt issuance costs	(544)	(348)
Total long-term debt	439,956	395,152
Less current portion	7,500	22,000
Long-term portion	432,456	373,152
Term Loan
Line of Credit Facility [Line Items]
Long-term debt	150,000	72,500
Revolving Credit Facility
Line of Credit Facility [Line Items]
Long-term debt	$ 290,500	$ 316,000