Share-Based Compensation - Schedule of Share-based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total share-based compensation expense	$ 5,585	$ 2,488	$ 11,553	$ 9,169
Direct cost of revenues
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total share-based compensation expense	2,427	1,183	6,206	7,021
Selling, general and administrative expenses
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total share-based compensation expense	3,158	1,209	5,347	2,052
Special charges
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total share-based compensation expense	$ 0	$ 96	$ 0	$ 96