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Subsequent Event - Additional Information (Detail) - USD ($)
$ in Thousands
Jul. 17, 2017
Jun. 30, 2017
Dec. 31, 2016
Jun. 30, 2016
Dec. 31, 2015
Subsequent Event [Line Items]          
Cash and Cash Equivalents, at Carrying Value   $ 178,633 $ 163,467 $ 187,600 $ 178,853
Summit Truck Group [Member] | Subsequent Event [Member]          
Subsequent Event [Line Items]          
Cash and Cash Equivalents, at Carrying Value $ 14,200