Schedule of Adjustments to Condensed Consolidated Balance Sheet Under New Guidance (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets:
Unbilled - collaboration and license revenue	$ 6,491	$ 6,694
Trade and other receivables, net	3,421	2,706	$ 3,750
Prepaid expenses and other current assets	0	0
Liabilities:
Deferred revenue, current portion	4,928	6,354	11,169
Deferred revenue, long-term	5,194	1,269	18,798
Stockholders’ equity:
Accumulated deficit	(1,365,853)	(1,175,481)	$ (1,204,519)
As Originally Reported | Accounting Standards Update 2014-09
Assets:
Prepaid expenses and other current assets	847	2,706
Liabilities:
Deferred revenue, current portion	5,726	11,169
Deferred revenue, long-term	25,316	18,798
Stockholders’ equity:
Accumulated deficit	(1,393,264)	(1,204,519)
Effect of Change | Accounting Standards Update 2014-09
Assets:
Unbilled - collaboration and license revenue	6,491	6,694
Trade and other receivables, net		2,706
Prepaid expenses and other current assets	(847)	(2,706)
Liabilities:
Deferred revenue, current portion	(798)	(4,815)
Deferred revenue, long-term	(20,122)	(17,529)
Stockholders’ equity:
Accumulated deficit	$ 27,411	$ 29,038