Impact on Condensed Consolidated Balance Sheet and Consolidated Statement of Comprehensive Loss for Adoption of New Revenue Standard (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue, current portion	$ 35,855		$ 7,242	$ 41,705
Deferred revenue, net of current portion	7,676		9,328	43,075
Accumulated deficit	(2,220,689)		(2,079,475)	$ (2,147,685)
Net revenues from collaborators	21,899	$ 18,960
Net loss	$ (141,214)	$ (107,290)
Net loss per common share - basic and diluted	$ (1.41)	$ (1.25)
Balances Without Adoption of New Revenue Standard
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Net revenues from collaborators	$ 55,026
ASU 2014-09 Revenue from Contracts with Customers | Balances Without Adoption of New Revenue Standard
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue, current portion	52,860
Deferred revenue, net of current portion	25,669
Accumulated deficit	(2,255,772)
Net revenues from collaborators	55,026
Net loss	$ (108,087)
Net loss per common share - basic and diluted	$ (1.08)
ASU 2014-09 Revenue from Contracts with Customers | Effect of Change Higher/(Lower)
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue, current portion	$ (17,005)		(34,463)
Deferred revenue, net of current portion	(17,993)		(33,747)
Accumulated deficit	(35,083)		$ 68,210
Net revenues from collaborators	(33,127)
Net loss	$ 33,127
Net loss per common share - basic and diluted	$ 0.33