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Asset Retirement Obligation - Schedule of Asset Retirement Obligation (Detail) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Asset Retirement Obligation Disclosure [Abstract]    
Balance at January 1, $ 6,374 $ 9,679
Accretion 229 458
Payments (2,824) (1,255)
Gain (1,255)  
Balance at December 31, $ 4,748 $ 6,374