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Long-Term Debt - Additional information (Detail) - USD ($)
3 Months Ended 9 Months Ended
Apr. 16, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Apr. 17, 2018
Dec. 31, 2017
Debt Instrument [Line Items]            
Maximum consolidated debt reduction for unrestricted cash and cash equivalents for debt covenant calculation     $ 200,000,000      
Additional interest expense   $ 369,000 458,000 $ 1,089,000    
Minimum [Member]            
Debt Instrument [Line Items]            
Reduction of consolidated debt in the debt ratio calculation     $ 50,000,000      
Including Acquisition Bridge Debt | Maximum            
Debt Instrument [Line Items]            
Debt covenant     350.00%      
Excluding Acquisition Bridge Debt | Maximum            
Debt Instrument [Line Items]            
Debt covenant     375.00%      
Revolving Facility            
Debt Instrument [Line Items]            
Credit facility commitment     $ 700,000,000      
Senior unsecured revolving facility, maturity period     5 years      
Outstanding letters of credit   1,963,000 $ 2,301,000 1,963,000   $ 2,301,000
Trade Receivable Facility            
Debt Instrument [Line Items]            
Credit facility commitment         $ 400,000,000  
Debt instrument maturity period     Sep. 25, 2019      
Credit facility borrowing base   $ 402,754,000 $ 465,217,000 $ 402,754,000   $ 338,784,000
Trade Receivable Facility | London Interbank Offered Rate(LIBOR)            
Debt Instrument [Line Items]            
Basis spread on variable rate     0.725%      
6.60% Senior Notes, Due 2018            
Debt Instrument [Line Items]            
Maturity date Apr. 16, 2018          
Repayments of credit facility $ 300,000,000          
Interest rate on notes 6.60%   6.60%