Warrants - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended			9 Months Ended
	Aug. 31, 2015	Jul. 31, 2015	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2013
Common Stock Warrants [Line Items]
Placement warrants not excercised and remained outstanding			3,022,581			3,022,581
(Gain) loss related to change in fair value						$ (116)	$ 6,739
Equity Classified Common Stock Warrants
Common Stock Warrants [Line Items]
Warrants issued								128,231
Exercise price								$ 5.84
Common stock warrants, expiration date						Dec. 16, 2023
2015 Placement Equity Classified Common Stock Warrants | Insiders
Common Stock Warrants [Line Items]
Warrants issued	198,760	198,760
Exercise price	$ 5.00	$ 5.00
Common stock warrants, expiry term	5 years	5 years
Number of warrant exercised						159,010
Stock issued during period						92,487
Placement warrants not excercised and remained outstanding			39,750			39,750
Equity Classified Common Stock 2018 Offering Warrants
Common Stock Warrants [Line Items]
Warrants issued				1,418,116
Exercise price				$ 8.31
Common stock warrants, expiration date				Mar. 31, 2025
Equity Classified Common Stock 2018 Offering Warrants | 2018 Direct Registered Offering
Common Stock Warrants [Line Items]
Proceed from private placement and equity issuances, gross				$ 59,100
Fair value of warrants upon issuance				7,400
Allocated portion of proceeds from issuance of stock and warrants				$ 6,600
Equity Classified Common Stock 2018 Offering Warrants | 2018 Direct Registered Offering | Expected Term
Common Stock Warrants [Line Items]
Warrants, fair value measurement inputs				7 years
Equity Classified Common Stock 2018 Offering Warrants | 2018 Direct Registered Offering | Expected Volatility
Common Stock Warrants [Line Items]
Warrants, fair value measurement inputs				62.50%
Equity Classified Common Stock 2018 Offering Warrants | 2018 Direct Registered Offering | Risk-free Interest Rate
Common Stock Warrants [Line Items]
Warrants, fair value measurement inputs				2.80%
Equity Classified Common Stock 2018 Offering Warrants | 2018 Direct Registered Offering | Expected Dividend Yield
Common Stock Warrants [Line Items]
Warrants, fair value measurement inputs				0.00%
2016 and 2017 Placement Warrants
Common Stock Warrants [Line Items]
(Gain) loss related to change in fair value			$ 6,700		$ (2,300)	$ (400)	$ 6,700