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Quarterly Results of Operations - Summary of Quarterly Results of Operations (Parenthetical) (Detail) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2017
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]        
Impairment charges $ 280,100 $ 340,480 $ 110,906 $ 279,021