Estimated Fair Value of Debt (Detail) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2013
Debt Instrument [Line Items]  
Debt instrument, fair value $ 559,946
Revolving credit facility
 
Debt Instrument [Line Items]  
Debt instrument, fair value 135,990
2018 Notes
 
Debt Instrument [Line Items]  
Debt instrument, fair value 404,000
Vehicle Financings
 
Debt Instrument [Line Items]  
Debt instrument, fair value $ 19,956