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Intangible Assets - Additional Information (Detail) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]          
Goodwill $ 620   $ 620   $ 620
Amortization expense $ 4,900 $ 6,000 $ 16,500 $ 15,800