Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Summary Of Significant Accounting Policies [Line Items]
Accumulated deficit	$ (736,593)		$ (712,442)
ASU 2014-09
Summary Of Significant Accounting Policies [Line Items]
Accumulated deficit		$ (720,573)
Difference between Revenue Guidance in Effect before and after Topic 606 | ASU 2014-09
Summary Of Significant Accounting Policies [Line Items]
Accumulated deficit	$ 9,582	$ (8,131)