Significant Accounting Policies - Summary of Impact of Adoption of Topic 606 on Contract Liabilities and Accumulated Deficit (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Significant Accounting Policies [Line Items]
Current portion of deferred revenue	$ 7,000
Long-term portion of deferred revenue	12,272
Accumulated deficit	(138,286)		$ (122,828)	[1]
Before Adoption of Topic 606
Significant Accounting Policies [Line Items]
Current portion of deferred revenue	6,250		6,250
Long-term portion of deferred revenue	$ 15,421		16,984
Accumulated deficit			$ (122,828)
ASC 606
Significant Accounting Policies [Line Items]
Current portion of deferred revenue		$ 7,000
Long-term portion of deferred revenue		14,022
Accumulated deficit		(120,616)
ASC 606 | Adjustment due to The Adoption of Topic 606
Significant Accounting Policies [Line Items]
Current portion of deferred revenue		750
Long-term portion of deferred revenue		(2,962)
Accumulated deficit		$ 2,212

[1] The Condensed Consolidated Balance Sheet as of December 31, 2018 has been derived from the audited financial statements as of that date.