Restructuring - Summary of Net Restructuring Charges Within Consolidated Statement of Operation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring Cost And Reserve [Line Items]
Total restructuring charges	$ 3,184	$ 1,938	$ 36,481
Cost of Revenue [Member]
Restructuring Cost And Reserve [Line Items]
Total restructuring charges			1,066
Research and Development [Member]
Restructuring Cost And Reserve [Line Items]
Total restructuring charges	2,347	124	14,081
Sales and Marketing [Member]
Restructuring Cost And Reserve [Line Items]
Total restructuring charges	149		787
General and Administrative [Member]
Restructuring Cost And Reserve [Line Items]
Total restructuring charges	$ 688	$ 1,814	$ 20,547