Term Loan - Narrative (Details) - USD ($)
3 Months Ended 6 Months Ended 15 Months Ended
Feb. 10, 2017
Nov. 10, 2015
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Feb. 10, 2017
Debt Instrument [Line Items]              
Term loan     $ 147,375,000   $ 147,375,000    
Debt issuance cost         370,000 $ 0  
Interest expense     3,300,000 $ 3,707,000 6,794,000 $ 7,339,000  
Senior Secured Debt | Credit Agreement              
Debt Instrument [Line Items]              
Debt instrument term   3 years          
Debt instrument, face amount   $ 150,000,000          
Debt instrument, extension of term 1 year            
Periodic payment of principal         375,000    
Term loan     $ 147,400,000   $ 147,400,000    
Debt issuance cost $ 370,000           $ 4,800,000
Percentage of debt discount   1.00%          
Debt instrument covenant, maximum debt-to-total capitalization ratio         35.00%    
Debt instrument covenant, maximum risk-to-capital ratio         22.0    
Debt instrument covenant, minimum liquidity requirement         $ 28,600,000    
Senior Secured Debt | Credit Agreement | Eurodollar              
Debt Instrument [Line Items]              
Variable rate floor         1.00%    
Basis spread on variable rate         6.75%    
Interest rate during period         7.87%