Quarterly report pursuant to Section 13 or 15(d)

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

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Fair Value of Financial Instruments - Fair Values and Related Carrying Values of Debt Instruments (Detail) - USD ($)
$ in Thousands
Sep. 30, 2017
Dec. 31, 2016
Carrying Amount [Member]    
Long-term Debt    
Long term debt Fair value $ 585,000 $ 585,000
Carrying Amount [Member] | 6.75% Senior Notes, due July 2022 [Member]    
Long-term Debt    
Long term debt Fair value 360,000 360,000
Carrying Amount [Member] | 7.50% Senior Notes, due August 2020 [Member]    
Long-term Debt    
Long term debt Fair value 225,000 225,000
Fair Value [Member]    
Long-term Debt    
Long term debt Fair value 490,500 512,775
Fair Value [Member] | 6.75% Senior Notes, due July 2022 [Member]    
Long-term Debt    
Long term debt Fair value 288,000 311,400
Fair Value [Member] | 7.50% Senior Notes, due August 2020 [Member]    
Long-term Debt    
Long term debt Fair value $ 202,500 $ 201,375