Organization - Additional Information (Detail) $ / shares in Units, $ in Thousands	1 Months Ended			3 Months Ended
	Apr. 30, 2019 USD ($) $ / shares shares	Feb. 28, 2019 USD ($)	Aug. 21, 2018 USD ($) shares	Jun. 30, 2019	Mar. 31, 2019 USD ($) Subsidiary shares	Mar. 31, 2018 shares	Dec. 31, 2018 USD ($) shares
Organization [Line Items]
Number of subsidiaries | Subsidiary					3
Cash, cash equivalents and marketable securities					$ 23,483		$ 24,427
Working capital					7,400
Accumulated deficit					$ 594,454		$ 595,009
Common stock, shares issued | shares					139,000,000		126,485,000
Underwritten Public Offering
Organization [Line Items]
Common stock, shares issued | shares			2,500,000
Net proceeds from issuance of common stock			$ 5,100
Underwritten Public Offering | Subsequent Event
Organization [Line Items]
Common stock, shares issued | shares	21,739,131
Net proceeds from issuance of common stock	$ 22,800
EUSA | Marketing Approval in Spain and Unite Kingdom
Organization [Line Items]
Milestone payment received		$ 2,000
Kyowa Hakko Kirin | Scenario Forecast
Organization [Line Items]
Percentage of sublicense fee payable				30.00%
Common Stock
Organization [Line Items]
Cash, cash equivalents and marketable securities					$ 23,500
Warrants to purchase of common stock | shares						24,000
Common Stock | Underwritten Public Offering | Subsequent Event
Organization [Line Items]
Warrants to purchase of common stock | shares	3,260,869
Shares issued, price per share | $ / shares	$ 1.14
Warrant issued, price per warrants | $ / shares	$ 0.01
Proceeds from issuance of warrants	$ 25,000
Net proceeds from issuance of common stock	$ 22,800
Offering Warrants | Underwritten Public Offering | Subsequent Event
Organization [Line Items]
Common stock, shares issued | shares	25,000,000