Annual report pursuant to Section 13 and 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
Dec. 31, 2017
Dec. 31, 2016
Jan. 22, 2014
6.75% Notes      
Long-term Debt      
Debt instrument fixed interest rate 6.75%   6.75%
Carrying Amount      
Long-term Debt      
Long-term Debt $ 585,000 $ 585,000  
Carrying Amount | 6.75% Notes      
Long-term Debt      
Long-term Debt 360,000 360,000  
Carrying Amount | 7.50% Notes      
Long-term Debt      
Long-term Debt 225,000 225,000  
Fair Value      
Long-term Debt      
Long-term Debt 502,538 512,775  
Fair Value | 6.75% Notes      
Long-term Debt      
Long-term Debt 296,100 311,400  
Fair Value | 7.50% Notes      
Long-term Debt      
Long-term Debt $ 206,438 $ 201,375