Segment Information and Geographic Data - Additional Information (Detail) - segment	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Revenues from External Customers and Long-Lived Assets [Line Items]
Reportable segments	2
Customer A | Customer Concentration Risk | Accounts Receivable
Revenues from External Customers and Long-Lived Assets [Line Items]
Concentration risk percentage	19.50%	19.90%
Customer B | Customer Concentration Risk | Accounts Receivable
Revenues from External Customers and Long-Lived Assets [Line Items]
Concentration risk percentage	14.00%	14.00%
Customer C | Customer Concentration Risk | Accounts Receivable
Revenues from External Customers and Long-Lived Assets [Line Items]
Concentration risk percentage	11.70%	12.90%