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Long-Term Debt - Summary of Components of Debt Obligations (Detail) - USD ($)
Jun. 30, 2018
Dec. 31, 2017
Debt Instrument [Line Items]    
Total debt $ 375,000,000 $ 400,000,000
Less: deferred debt issue costs (3,338,000) (3,716,000)
Long-term debt, net 371,662,000 396,284,000
Long-term debt, current portion 0 0
Senior Notes | 6.0% senior notes due 2022    
Debt Instrument [Line Items]    
Total debt 300,000,000 300,000,000
Line of Credit | Credit facility    
Debt Instrument [Line Items]    
Total debt $ 75,000,000 $ 100,000,000