Company Overview - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended
	Apr. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	[1]	Mar. 31, 2018	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Cash and cash equivalents		$ 24,811	$ 13,696		$ 21,365	$ 26,977
Accumulated deficit		$ 665,329	$ 659,469
Amended Loan Agreement [Member] | Subsequent Event [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Repayment of remaining obligations	$ 5,900

[1] The condensed consolidated balance sheet as of December 31, 2018, has been derived from the audited financial statements as of that date included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018.