Basis of Presentation and Summary of Significant Accounting Policies - Summary of Impacts of Adopting the New Standard on Balance Sheet for Adoption Date (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
ASSETS
Deferred costs, current	$ 4,452		$ 0
Other assets including non-current deferred cost	15,455		1,593
LIABILITIES
Deferred revenue, current	121,818		126,174
Deferred revenue	34,575		33,081
STOCKHOLDERS' EQUITY:
Accumulated deficit	(246,845)		$ (256,537)
Topic 606 [Member]
ASSETS
Deferred costs, current		$ 3,755
Other assets including non-current deferred cost		13,749
LIABILITIES
Deferred revenue, current		122,015
Deferred revenue		33,678
STOCKHOLDERS' EQUITY:
Accumulated deficit		(237,064)
Impact of Adoption [Member] | Topic 606 [Member]
ASSETS
Deferred costs, current	(4,452)	3,755
Other assets including non-current deferred cost	(14,043)	12,156
LIABILITIES
Deferred revenue, current	4,402	(4,159)
Deferred revenue	204	597
STOCKHOLDERS' EQUITY:
Accumulated deficit	$ (23,101)	$ 19,473