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Debt and Credit Facilities - Additional Information (Detail) - USD ($)
Apr. 12, 2017
Mar. 31, 2018
Mar. 22, 2018
Dec. 31, 2017
Term Loan Facility | Line of Credit        
Debt Instrument [Line Items]        
Secured term loan facility $ 175,000,000      
Accrued interest   $ 100,000    
Term Loan Facility | Secured Debt        
Debt Instrument [Line Items]        
Debt instrument fee   2,600,000    
Debt instrument discount   2,900,000    
Long-term debt   166,150,000   $ 166,949,000
Third ARLS Agreement | Line of Credit | Revolving Credit Facility        
Debt Instrument [Line Items]        
Accrued interest   100,000    
Debt instrument fee   900,000    
Availability of borrowing   55,800,000    
Outstanding borrowings   $ 7,500,000    
Interest rate (as a percent)   5.25% 5.00%  
Third ARLS Agreement | Line of Credit | Letter of Credit        
Debt Instrument [Line Items]        
Outstanding borrowings   $ 1,700,000   $ 2,100,000
Borrowing availability threshold $ 5,000,000      
Borrowing availability threshold (as a percent) 10.00%