Private Placement and Registered Direct Offering - Additional Information (Detail)					3 Months Ended			12 Months Ended
	Jun. 11, 2018 USD ($) $ / shares shares	May 11, 2018 USD ($) $ / shares shares	Mar. 22, 2018 $ / shares shares	Mar. 19, 2018	Mar. 31, 2019 USD ($) $ / shares shares	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)	May 07, 2018 USD ($)
Class Of Warrant Or Right [Line Items]
Warrants issued, exercise price | $ / shares					$ 18.15
Proceeds from issuance of private placement					$ 10,000,000
Offering costs					$ 226,000
Stock price | $ / shares					$ 32.52
Common stock no par value | $ / shares
Initial loss recognized on liabilities					$ 4,000,000
Liabilities marked to market value							$ 15,900,000
Additional loss/expense on liabilities							1,900,000
Offering cost, expense							$ 904,000
Issuance of placement agent warrants								$ 526,000
Proceeds from issuance initial public offering					50,000,000
Fair value of common stock warrants at inception					9,000,000
Warrants [Member]
Class Of Warrant Or Right [Line Items]
Issuance of placement agent warrants					$ 526,000
Placement Agent [Member] | Warrants [Member]
Class Of Warrant Or Right [Line Items]
Warrant issued, shares of common stock called by warrant | shares					15,038
Warrants issued, exercise price | $ / shares					$ 41.5625
Offering costs					$ 1,800,000
Warrant, exercisable term					5 years
Offering cost, expense					$ 1,800,000
June 2018 Placement Agent Warrants [Member]
Class Of Warrant Or Right [Line Items]
Warrant issued, shares of common stock called by warrant | shares					69,617
Warrants issued, exercise price | $ / shares					$ 12.568
Offering costs					$ 1,600,000
Aggregate agent fee paid					$ 980,000
Warrant, exercisable term					5 years
Offering cost, expense								721,000
Issuance of placement agent warrants					$ 427,000
Offering costs portion attributable to common stock					$ 912,000
Measurement Input, Price Volatility [Member]
Class Of Warrant Or Right [Line Items]
Volatility rate					1.00
Measurement Input, Risk Free Interest Rate [Member]
Class Of Warrant Or Right [Line Items]
Volatility rate					0.0263
Black Scholes Merton Model [Member]
Class Of Warrant Or Right [Line Items]
Stock price | $ / shares					$ 8.20
Black Scholes Merton Model [Member] | Measurement Input, Price Volatility [Member]
Class Of Warrant Or Right [Line Items]
Volatility rate					1.08
Black Scholes Merton Model [Member] | Measurement Input, Risk Free Interest Rate [Member]
Class Of Warrant Or Right [Line Items]
Volatility rate					0.0283
Common Stock Adjustment Feature Liability [Member] | Monte Carlo Simulation Model [Member]
Class Of Warrant Or Right [Line Items]
Fair value of liabilities					$ 3,800,000
March 2018 Warrant Liability [Member] | Monte Carlo Simulation Model [Member]
Class Of Warrant Or Right [Line Items]
Fair value of liabilities					10,200,000
June 2018 Warrant Liability [Member]
Class Of Warrant Or Right [Line Items]
Liabilities marked to market value					7,300,000
Additional loss/expense on liabilities					4,500,000
Proceeds from issuance of common stock					5,000,000
Proceeds from issuance of common stock and warrants gross					14,000,000
March 2018 Securities Purchase Agreement [Member]
Class Of Warrant Or Right [Line Items]
Shares of common stock issued | shares			1,201,636
Warrant issued, shares of common stock called by warrant | shares			1,282,832
Warrants issued, exercise price | $ / shares			$ 10.7258
June 2018 Purchase Agreement [Member]
Class Of Warrant Or Right [Line Items]
Offering costs					1,200,000
Proceeds from issuance of common stock and warrants gross					14,000,000
Proceeds from issuance of common stock and warrants net					12,800,000
March 2018 Private Placement [Member]
Class Of Warrant Or Right [Line Items]
Proceeds from issuance of private placement					8,700,000
Proceeds from offering costs of private placement, gross					10,000,000
Offering costs					1,300,000
Liabilities marked to market value									$ 8,400,000
Additional loss/expense on liabilities						$ 2,400,000
Reclassification of financing liabilities to stockholders equity						$ 8,400,000
March 2018 Private Placement [Member] | Warrants [Member]
Class Of Warrant Or Right [Line Items]
Offering costs					458,000
March 2018 Private Placement [Member] | Placement Agent [Member]
Class Of Warrant Or Right [Line Items]
Aggregate agent fee paid					850,000
March 2018 Private Placement [Member] | March 2018 Warrant Liability [Member]
Class Of Warrant Or Right [Line Items]
Liabilities marked to market value					6,300,000
Additional loss/expense on liabilities					$ 4,000,000
March 2018 Private Placement [Member] | March 2018 Securities Purchase Agreement [Member]
Class Of Warrant Or Right [Line Items]
Shares of common stock issued | shares			300,752
Warrant issued, shares of common stock called by warrant | shares			300,752
Warrants issued, exercise price | $ / shares			$ 45.75
Warrants expiration period				5 years
June 2018 Offering [Member]
Class Of Warrant Or Right [Line Items]
Issuance of placement agent warrants								$ 427,000
June 2018 Offering [Member] | June 2018 Purchase Agreement [Member]
Class Of Warrant Or Right [Line Items]
Shares of common stock issued | shares	1,392,345
Stock price | $ / shares	$ 9.93
Proceeds from issuance of common stock	$ 13,800,000
Offering closing period	Jun. 14, 2018
June 2018 Private Placement [Member] | Warrants [Member]
Class Of Warrant Or Right [Line Items]
Warrant issued, shares of common stock called by warrant | shares		1,392,345
Warrants issued, exercise price | $ / shares		$ 9.94
Warrants expiration period		5 years 6 months
Proceeds from offering costs of private placement, gross		$ 174,000
Class of warrant or right number of securities called by warrants or rights, per share | $ / shares		$ 0.125