Comparison of Reported Condensed Consolidated Balance Sheet Under New Guidance (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets:
Unbilled - collaboration and license revenue	$ 9,872	$ 6,694
Trade and other receivables, net	1,545
Prepaid expenses and other current assets	0	0
Liabilities:
Deferred revenue, current portion	2,358	6,354	$ 11,169
Deferred revenue, long-term	5,085	1,269	18,798
Stockholders’ equity:
Accumulated deficit	(1,437,156)	(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	1,545	2,706
Liabilities:
Deferred revenue, current portion	5,157	11,169
Deferred revenue, long-term	24,298	18,798
Stockholders’ equity:
Accumulated deficit	(1,469,041)	(1,204,519)
Effect of Change | Accounting Standards Update 2014-09
Assets:
Unbilled - collaboration and license revenue	9,872	6,694
Trade and other receivables, net	1,545
Prepaid expenses and other current assets	(1,545)	(2,706)
Liabilities:
Deferred revenue, current portion	(2,800)	(4,815)
Deferred revenue, long-term	(19,213)	(17,529)
Stockholders’ equity:
Accumulated deficit	$ 31,885	$ 29,038