Going Concern - Additional Information (Detail) - USD ($)		12 Months Ended
	Jan. 07, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Unrestricted cash and cash equivalents		$ 21,524,000	$ 185,606,000	$ 35,688,000	$ 65,086,000
Aggregate principal amount outstanding to be redeemed			$ 40,000,000
Substantial doubt about going concern, conditions and events		The consummation of the asset sale with Ipsen is contingent upon approval by the Company’s stockholders as well as other customary closing conditions. If the asset sale is not consummated, the Company will not receive the $575.0 million upfront cash payment from Ipsen, and the Company will need to obtain additional funding through public or private debt or equity financings, through existing or new collaboration arrangements, or through divestitures of its assets.
Substantial doubt about going concern, within one year		true
Subsequent Event [Member] | Asset Sale Agreement [Member] | Minimum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Special cash dividend to be paid	$ 200,000,000
Subsequent Event [Member] | Asset Sale Agreement [Member] | 2022 Notes [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Aggregate principal amount outstanding to be redeemed	175,000,000
Additional premium payment	20,100,000
Subsequent Event [Member] | Ipsen [Member] | Asset Sale Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront cash payment to be received	575,000,000
Subsequent Event [Member] | Baxalta [Member] | License and Collaboration Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Net milestone payments expected to be received	$ 33,000,000