Segments, Concentrations and Geographic Information - Additional Information (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2018 customer	Jun. 30, 2017 customer	Jun. 30, 2018 segment
Revenues from External Customers and Long-Lived Assets [Line Items]
Number of business segments | segment			3
Sales Revenue, Net [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Number of major customers	0	0
Gearing [Member] | Sales Revenue, Net [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Number of major customers	1
Gearing [Member] | Sales Revenue, Net [Member] | Customer Concentration Risk [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Concentration risk (as percent)	10.00%