Quarterly report pursuant to Section 13 or 15(d)

Fair Value of Measurements - Fair Values and Related Carrying Values of Debt Instruments (Detail)

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Fair Value of Measurements - Fair Values and Related Carrying Values of Debt Instruments (Detail) - USD ($)
$ in Thousands
Sep. 30, 2018
Dec. 31, 2017
Jan. 22, 2014
Jul. 30, 2013
6.75% Senior Notes, due July 2022        
Long-term debt        
Percentage of notes guaranteed by restricted subsidiaries     6.75%  
7.50% Senior Notes, due August 2020        
Long-term debt        
Percentage of notes guaranteed by restricted subsidiaries       7.50%
Carrying Amount        
Long-term debt        
Long term debt Fair value $ 585,000 $ 585,000    
Carrying Amount | 6.75% Senior Notes, due July 2022        
Long-term debt        
Long term debt Fair value 360,000 360,000    
Carrying Amount | 7.50% Senior Notes, due August 2020        
Long-term debt        
Long term debt Fair value 225,000 225,000    
Fair Value        
Long-term debt        
Long term debt Fair value 482,850 502,538    
Fair Value | 6.75% Senior Notes, due July 2022        
Long-term debt        
Long term debt Fair value 282,600 296,100    
Fair Value | 7.50% Senior Notes, due August 2020        
Long-term debt        
Long term debt Fair value $ 200,250 $ 206,438