Warrant Liability - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Jun. 13, 2017	Jul. 05, 2016
Warrant Liability [Line Items]
Derivative Liability, Fair Value, Gross Liability	$ 0	$ 2,900		$ 4,600
Increase (Decrease) in Derivative Liabilities	2,400	$ 1,700
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	(175)
Warrants 2016 [Member]
Warrant Liability [Line Items]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights			127,941
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	200
Extinguishment of Debt, Amount	$ 400
Health care Institutional Investors
Warrant Liability [Line Items]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights		294,118
Class of Warrant or Right, Exercise Price of Warrants or Rights		$ 23.00
Hc Wainwright Co Llc
Warrant Liability [Line Items]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights		25,000
Class of Warrant or Right, Exercise Price of Warrants or Rights		$ 24.60