Long-term Debt (Detail) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2013
Dec. 31, 2012
Debt Instrument [Line Items]    
Credit facility $ 335,000 $ 162,000
Senior notes 400,000 400,000
Unamortized premium on senior notes 1,671 1,865
Total long-term debt $ 736,671 $ 563,865