Debt Obligations - Narrative (Details) - USD ($)
1 Months Ended 3 Months Ended 6 Months Ended
May 24, 2018
Jun. 30, 2018
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Nov. 10, 2015
Debt Instrument [Line Items]              
Interest expense     $ 5,560,000 $ 3,300,000 $ 8,979,000 $ 6,794,000  
Term loan   $ 150,000,000 150,000,000   150,000,000    
Secured Debt | 2018 Term Loan              
Debt Instrument [Line Items]              
Debt instrument face amount $ 150,000,000            
Debt instrument term 5 years            
Interest rate during period   6.84%          
Frequency of periodic payment Quarterly            
Periodic payment of principal $ 375,000            
Prepayment premium (percent) 1.00%            
Prepayment penalty time period 6 months            
Interest expense         9,000,000    
Debt issuance costs $ 1,800,000            
Original issue discount $ 986,000            
Unamortized issuance cost and original issue discount   $ 2,700,000 2,700,000   2,700,000    
Term loan   $ 150,000,000 150,000,000   150,000,000    
Debt instrument covenant, maximum debt-to-total capitalization ratio   35.00%          
Secured Debt | 2018 Term Loan | Eurodollar              
Debt Instrument [Line Items]              
Variable rate floor   1.00%          
Basis spread on variable rate   4.75%          
Senior Secured Debt | 2015 Term Loan              
Debt Instrument [Line Items]              
Debt instrument face amount             $ 150,000,000
Costs related to extinguishment of debt         2,200,000    
Revolving Credit Facility | 2018 Revolving Credit Facility              
Debt Instrument [Line Items]              
Debt instrument term 3 years            
Credit facility borrowing capacity $ 85,000,000            
Debt issuance costs $ 1,500,000            
Debt instrument covenant, maximum debt-to-total capitalization ratio   35.00%          
Borrowings outstanding   $ 0 0   0    
Commitment fee (percent)   0.50%          
Commitment fees in interest expense   $ 46,000          
Remaining net debt issuance costs   1,500,000 1,500,000   1,500,000    
Accumulated amortization, debt issuance costs   $ 42,000 $ 42,000   $ 42,000    
Revolving Credit Facility | 2018 Revolving Credit Facility | Minimum              
Debt Instrument [Line Items]              
Commitment fee (percent) 0.30%            
Revolving Credit Facility | 2018 Revolving Credit Facility | Maximum              
Debt Instrument [Line Items]              
Commitment fee (percent) 0.60%            
Revolving Credit Facility | 2018 Revolving Credit Facility | Base Rate              
Debt Instrument [Line Items]              
Variable rate floor 1.00%            
Revolving Credit Facility | 2018 Revolving Credit Facility | Base Rate | Minimum              
Debt Instrument [Line Items]              
Basis spread on variable rate 1.00%            
Revolving Credit Facility | 2018 Revolving Credit Facility | Base Rate | Maximum              
Debt Instrument [Line Items]              
Basis spread on variable rate 2.50%            
Revolving Credit Facility | 2018 Revolving Credit Facility | Eurodollar              
Debt Instrument [Line Items]              
Variable rate floor 0.00%            
Revolving Credit Facility | 2018 Revolving Credit Facility | Eurodollar | Minimum              
Debt Instrument [Line Items]              
Basis spread on variable rate 2.00%            
Revolving Credit Facility | 2018 Revolving Credit Facility | Eurodollar | Maximum              
Debt Instrument [Line Items]              
Basis spread on variable rate 3.50%