Nature of the Business and Summary of Significant Accounting Policies - Additional Information (Detail)			3 Months Ended								12 Months Ended
	Aug. 11, 2017 shares	Apr. 03, 2017 USD ($)	Dec. 31, 2017 USD ($) Program shares	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) shares	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) Program Segment Customer Region shares	Dec. 31, 2016 USD ($) Customer shares	Dec. 31, 2015 USD ($) Customer	Sep. 05, 2017 shares	Dec. 31, 2014 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of development programs active | Program			2								2
Accumulated deficit			$ 482,771,000				$ 954,799,000				$ 482,771,000	$ 954,799,000
Net loss from continuing operations			11,829,000	$ 5,323,000	$ 29,646,000	$ 29,206,000	40,091,000	$ 26,845,000	$ 51,633,000	$ 37,715,000	76,004,000	156,284,000	$ 151,619,000
Cash in continuing operations for operating activities											104,270,000	122,935,000	109,828,000
Cash and cash equivalents			$ 93,441,000				$ 21,524,000				$ 93,441,000	$ 21,524,000	185,606,000		$ 35,688,000
Number of operating segments | Segment											1
Number of geographic regions | Region											1
Reverse stock split, conversion ratio	0.1
Reverse stock split description	Reverse Split, every ten shares of common stock issued and outstanding was converted into one share of common stock										Reverse Split, every ten shares of common stock issued and outstanding was converted into one share of common stock
Common stock, shares issued | shares	132,800,000		13,343,000				13,020,000				13,343,000	13,020,000		13,280,000
Common stock, shares outstanding | shares	132,800,000		13,343,000				13,020,000				13,343,000	13,020,000		13,280,000
Number of fractional shares issued | shares														0
Common stock, shares authorized | shares	200,000,000		20,000,000				20,000,000				20,000,000	20,000,000		20,000,000
Preferred stock, shares issued | shares			0				0				0	0		0
Preferred stock, shares outstanding | shares			0				0				0	0		0
Original maturities											Three months or less
Restricted cash			$ 800,000				$ 800,000				$ 800,000	$ 800,000
Marketable securities			0				$ 0				$ 0	0
Performance period											5 years
Tax incentive awarded											$ 3,800,000
State research and development tax credits monetized											3,400,000
Amount of tax incentives required to repay			$ 1,400,000								1,400,000
Amount of benefit recognized											$ 0	$ 100,000	$ 700,000
Customer Concentration Risk | Sales Revenue, Net [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of customer | Customer											0	0	0
Customer Concentration Risk | Accounts Receivable [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of customer | Customer											0	0	0
Maximum [Member] | Silver Creek Pharmaceuticals Inc [Member]
Summary Of Significant Accounting Policies [Line Items]
Ownership interest (as a percent)				50.00%
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Expected remaining maturities period of marketable securities classified as available-for-sale											3 months
Ipsen [Member] | Asset Sale Agreement [Member]
Summary Of Significant Accounting Policies [Line Items]
Upfront cash payment received		$ 575,000,000
Working capital adjustments received		5,700,000
Ipsen [Member] | Asset Sale Agreement [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Additional payments receivable on achievement of certain milestone events		450,000,000
Baxalta [Member] | License and Collaboration Agreements [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Net milestone payments expected to be received		$ 33,000,000