Comparison of Reported Consolidated Balance Sheet Under New Guidance (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets:
Unbilled - collaboration and license revenue	$ 9,880	$ 6,694
Trade and other receivables, net	1,243	2,706
Liabilities:
Deferred revenue, current portion	1,847	6,354	$ 11,169
Deferred revenue, long-term	4,488	1,269	18,798
Stockholders’ equity:
Accumulated deficit	(1,525,704)	(1,175,481)	$ (1,204,519)
Balances Without the Adoption of ASC 606 | Accounting Standards Update 2014-09
Assets:
Prepaid expenses and other current assets	1,243	2,706
Liabilities:
Deferred revenue, current portion	4,589	11,169
Deferred revenue, long-term	22,695	18,798
Stockholders’ equity:
Accumulated deficit	(1,556,533)	(1,204,519)
Effect of Change | Accounting Standards Update 2014-09
Assets:
Unbilled - collaboration and license revenue	9,880	6,694
Trade and other receivables, net	1,243	2,706
Prepaid expenses and other current assets	(1,243)	(2,706)
Liabilities:
Deferred revenue, current portion	(2,742)	(4,815)
Deferred revenue, long-term	(18,207)	(17,529)
Stockholders’ equity:
Accumulated deficit	$ 30,829	$ 29,038