Quarterly report pursuant to Section 13 or 15(d)

Long-Term Debt - Prior Term Loan B and Revolving Credit Facility - Additional Information (Detail)

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Long-Term Debt - Prior Term Loan B and Revolving Credit Facility - Additional Information (Detail) - USD ($)
3 Months Ended 9 Months Ended
May 19, 2017
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Debt Instrument [Line Items]        
Interest expense, debt   $ 0   $ 200,000
Gains (losses) on extinguishment of debt, total     $ 234,000 (2,775,000)
Debt instrument, interest rate, stated percentage     4.58%  
Amortization of financing costs     $ 855,000 645,000
Term Loan B [Member]        
Debt Instrument [Line Items]        
Line of credit facility, maximum borrowing capacity     300,000,000  
Senior notes, non-current     298,500,000  
Interest expense, debt   0   100,000
Long-term debt, gross $ 258,000,000      
Debt instrument, unamortized discount 600,000      
Revolver [Member]        
Debt Instrument [Line Items]        
Line of credit facility, maximum borrowing capacity     $ 25,000,000  
Long-term line of credit, non-current 4,100,000      
Gains (losses) on extinguishment of debt, total 2,100,000      
Amortization of financing costs   $ 0   $ 26,000
Term Loan B and Revolver [Member]        
Debt Instrument [Line Items]        
Unamortized debt issuance expense $ 1,500,000