Long-Term Debt - Summary of Long-Term Debt (Details) - USD ($)		Jun. 30, 2019	Dec. 31, 2018	Sep. 29, 2017
Debt Instrument [Line Items]
Revolving credit facility		$ 340,000,000	$ 321,000,000
Second Lien Facility		200,000,000	200,000,000	$ 200,000,000
Long-term Debt		540,000,000	521,000,000
Debt Instrument, Unamortized Discount		(2,795,000)	(3,159,000)	(4,000,000.0)
Unamortized Debt Issuance Expense		(5,729,000)	(6,466,000)	$ (8,200,000)
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net		531,476,000	511,375,000
Unamortized Loan Commitment and Origination Fees and Unamortized Discounts or Premiums	[1],[2]	$ 8,524,000	$ 9,625,000

[1] Issuance costs of the Credit Facility, which represent costs attributable to the access to credit over its contractual term, have been presented as a component of Other assets (see Note 10) and are being amortized over the term of the Credit Facility using the straight-line method.

[2] Discount and issuance costs of the Second Lien Facility are being amortized over the term of the underlying loan using the effective-interest method