Acquisition - Additional Information (Detail) - Series of Individually Immaterial Business Acquisitions [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Total consideration transferred at fair value	$ 67,000	$ 10,300	$ 49,700
Acquired deferred revenue, impact on reported revenue	$ 2,856	$ 100	$ 800