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Property, Plant and Equipment - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Property, Plant and Equipment [Abstract]      
Depreciation expense $ 3.7us-gaap_Depreciation $ 2.0us-gaap_Depreciation $ 0.9us-gaap_Depreciation