Organization, Basis of Presentation and Summary of Significant Accounting Policies - Condensed Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue, current portion	$ 57,215		$ 28,345
Deferred revenue, noncurrent portion	137,731		29,244
Accumulated deficit	(531,189)		$ (495,479)
Topic 606 [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue, current portion		$ 29,626
Deferred revenue, noncurrent portion		26,846
Accumulated deficit		(494,362)
Adjustments [Member] | Topic 606 [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue, current portion	8,744	1,281
Deferred revenue, noncurrent portion	(3,581)	(2,398)
Accumulated deficit	(5,163)	1,117
Balances without adoption of Topic 606 [Member] | Topic 606 [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue, current portion	65,959	28,345
Deferred revenue, noncurrent portion	134,151	29,244
Accumulated deficit	$ (536,352)	$ (495,479)