Goodwill and Intangible Assets - Narrative (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	$ 83,164		$ 83,164	$ 83,164
Amortization expense	1,000	$ 500
Capitalized internal-use software costs for works in process	$ 800