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Property and Equipment - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Property Plant And Equipment [Abstract]      
Depreciation expense $ 13,400,000 $ 21,900,000 $ 24,800,000
Asset impairment charges $ 0 $ 1,200,000 $ 41,700,000