Related Party Transactions - Schedule of Amount of General and Administrative Costs and Expenses Recognized (Detail) (Omnibus Agreement [Member], USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Omnibus Agreement [Member]
     
Related Party Transaction [Line Items]      
General and administrative costs and expenses under omnibus agreement $ 24,372 $ 9,440 $ 1,771