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 ($)	Dec. 31, 2018 USD ($) shares	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) shares	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) Segment Region shares	Dec. 31, 2017 USD ($) shares	Sep. 05, 2017 shares
Summary Of Significant Accounting Policies [Line Items]
Accumulated deficit			$ 523,277,000				$ 482,771,000				$ 523,277,000	$ 482,771,000
Net loss from continuing operations			12,875,000	$ 12,341,000	$ 17,769,000	$ 17,782,000	$ 11,829,000	$ 5,323,000	$ 29,646,000	$ 29,206,000	60,767,000	76,004,000
Cash in continuing operations for operating activities											65,588,000	$ 84,146,000
Cash, cash equivalents and marketable securities			$ 71,300,000								$ 71,300,000
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
Common stock, shares issued | shares	132,800,000		13,343,000				13,343,000				13,343,000	13,343,000	13,280,000
Common stock, shares outstanding | shares	132,800,000		13,343,000				13,343,000				13,343,000	13,343,000	13,280,000
Number of fractional shares issued | shares													0
Common stock, shares authorized | shares	200,000,000		30,000,000				20,000,000				30,000,000	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			$ 600,000				$ 800,000				$ 600,000	$ 800,000
Other (expense) income recognized primarily related to proportionate share of losses from equity investment											3,230,000	1,433,000
ASU 2016-15 [Member]
Summary Of Significant Accounting Policies [Line Items]
Reclassification of debt extinguishment cost from cash outflow of operating activities to financing activities												20,100,000
Silver Creek Pharmaceuticals Inc [Member]
Summary Of Significant Accounting Policies [Line Items]
Other (expense) income recognized primarily related to proportionate share of losses from equity investment											$ 3,200,000	$ 1,400,000
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 original maturities period of marketable securities classified as available-for-sale											90 days
Asset Sale Agreement [Member] | Development and Commercialization Milestones [Member]
Summary Of Significant Accounting Policies [Line Items]
Maximum amount of milestone payments that can be received											$ 33,000,000
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
Ipsen [Member] | Asset Sale Agreement [Member] | Development and Commercialization Milestones [Member]
Summary Of Significant Accounting Policies [Line Items]
Maximum amount of milestone payments that can be received		33,000,000
Servier [Member] | Asset Sale Agreement [Member] | Development and Commercialization Milestones [Member]
Summary Of Significant Accounting Policies [Line Items]
Maximum amount of milestone payments that can be received		$ 33,000,000