Quarterly report pursuant to Section 13 or 15(d)

Long-Tem Debt - Schedule of Long-Term Debt (Details)

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Long-Tem Debt - Schedule of Long-Term Debt (Details) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Jan. 11, 2018
Mar. 31, 2019
Dec. 31, 2017
Dec. 31, 2018
Debt Instrument [Line Items]        
Total   $ 483,068   $ 412,682
Less: current portion of long-term debt   (3,293)   (3,293)
Less: unamortized debt discounts   (3,457)   (3,300)
Less: deferred financing costs   (3,781)   (3,994)
Total long-term debt   472,537   402,095
Syndicate of Lenders | Line of Credit        
Debt Instrument [Line Items]        
Total   $ 391,842   $ 322,666
Interest rate during period   7.50%   7.53%
Syndicate of Lenders | Line of Credit | LIBOR        
Debt Instrument [Line Items]        
Basis spread on variable rate   5.00% 5.00%  
Goldman Sachs Specialty Lending Group | Line of Credit        
Debt Instrument [Line Items]        
Interest rate during period   10.50%   10.50%
Goldman Sachs Specialty Lending Group | Line of Credit | Payment-in-Kind Interest Rate        
Debt Instrument [Line Items]        
Basis spread on variable rate   5.00% 5.00%  
Term Loan | Syndicate of Lenders | Line of Credit | LIBOR        
Debt Instrument [Line Items]        
Basis spread on variable rate 5.00%      
Term Loan | Goldman Sachs Specialty Lending Group | Line of Credit        
Debt Instrument [Line Items]        
Total   $ 91,226   $ 90,016