Schedule of Adjustments to Condensed Consolidated Balance Sheet Under New Guidance (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets:
Unbilled - collaboration and license revenue	$ 4,660	$ 6,694
Trade and other receivables, net	1,693	2,706	$ 3,750
Prepaid expenses and other current assets	14,569		9,010
Liabilities:
Deferred revenue, current portion	3,861	6,354	11,169
Deferred revenue, long-term	5,412	1,269	18,798
Stockholders’ equity:
Accumulated deficit	(1,259,660)	(1,175,481)	$ (1,204,519)
As originally reported | Accounting Standards Update 2014-09
Assets:
Prepaid expenses and other current assets	968	2,706
Liabilities:
Deferred revenue, current portion	9,547	11,169
Deferred revenue, long-term	23,064	18,798
Stockholders’ equity:
Accumulated deficit	(1,287,659)	(1,204,519)
Effect of change | Accounting Standards Update 2014-09
Assets:
Unbilled - collaboration and license revenue	4,660	6,694
Trade and other receivables, net		2,706
Prepaid expenses and other current assets	(968)	(2,706)
Liabilities:
Deferred revenue, current portion	(5,686)	(4,815)
Deferred revenue, long-term	(17,652)	(17,529)
Stockholders’ equity:
Accumulated deficit	$ 27,999	$ 29,038