Debt - Narrative (Details) - USD ($)		12 Months Ended
	Jul. 31, 2015	Dec. 31, 2018	Dec. 31, 2017	Jan. 31, 2019	Nov. 18, 2015
Line of Credit Facility [Line Items]
Accretion of debt issuance costs		$ 2,500,000	$ 2,400,000
Excess cash flows, repayment of debt, percentage		50.00%
Excess cash flows threshold for dividend		$ 5,000,000
Term Loan
Line of Credit Facility [Line Items]
Debt issuance costs incurred	$ 12,900,000	12,900,000
Unamortized deferred issuance costs		6,200,000	8,300,000
Face amount	$ 425,000,000.0
Amortization per year (as a percent)	1.00%
Outstanding loan balance		410,100,000
Revolving loan
Line of Credit Facility [Line Items]
Debt issuance costs incurred	$ 1,300,000
Maximum borrowing available	25,000,000.0
Outstanding loan balance		0
Letter-of-credit sub-facility
Line of Credit Facility [Line Items]
Maximum borrowing available	$ 10,000,000.0
Letters of credit issued, amount		600,000
Credit facility amount outstanding		0
Credit Facility
Line of Credit Facility [Line Items]
Outstanding loan balance		412,897,000
Cap on dividends paid and shares and warrants that can be repurchased per fiscal year under restrictive covenants		12,000,000.0			$ 12,000,000
Repayments of principal in next 12 months		6,419,000
Credit Facility | Alternate base rate
Line of Credit Facility [Line Items]
Margin of interest (as a percent)	3.75%
Credit Facility | LIBOR
Line of Credit Facility [Line Items]
Margin of interest (as a percent)	4.75%
Variable rate base minimum (as a percent)	1.00%
Level 2 | Term Loan
Line of Credit Facility [Line Items]
Fair value of long-term debt		397,100,000	$ 408,200,000
Prepayment due to excess cash flow provision | Term Loan
Line of Credit Facility [Line Items]
Repayments of principal in next 12 months		$ 0
Subsequent event | Revolving loan
Line of Credit Facility [Line Items]
Maximum borrowing available				$ 12,500,000