Schedule of Adoption of New Revenue Guidance Impact on Consolidated Statement of Cash Flows (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash Flows from Operating Activities
Net loss	$ (9,747)	$ (24,168)	$ (22,675)	$ (30,385)	$ (32,784)	$ (32,886)	$ (35,339)	$ (16,324)	$ (86,975)	$ (117,333)	$ 125,664
Changes in operating assets and liabilities:
Accounts receivable, net									(1,339)	(2,487)	(302)
Deferred costs from commercial product sales										96	309
Accrued expenses and other current liabilities									2,249	2,932	348
Deferred revenue, net										$ (381)	$ 3,419
Cash (used in) provided by operating activities									(37,731)
Adjustments | Accounting Standards Update 2014-09
Cash Flows from Operating Activities
Net loss									(267)
Changes in operating assets and liabilities:
Accounts receivable, net									2,567
Deferred costs from commercial product sales									470
Accrued expenses and other current liabilities									(751)
Deferred revenue, net									(899)
Cash (used in) provided by operating activities									1,120
Balances Without Adoption of Topic 606 | Accounting Standards Update 2014-09
Cash Flows from Operating Activities
Net loss									(87,242)
Changes in operating assets and liabilities:
Accounts receivable, net									1,228
Deferred costs from commercial product sales									470
Accrued expenses and other current liabilities									1,498
Deferred revenue, net									(899)
Cash (used in) provided by operating activities									$ (36,611)