Segment & Geographical Information - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017 operating_segment Segment
Segment Reporting [Abstract]
Number of operating segments	8
Number of operating segments, operations management	6
Number of operating segments, finance and accounting	1
Number of operating segments, company provides operations management services	6
Number of operating segments, non-operations management services	2
Number of reportable segments | Segment	2