Warrants - Additional Information (Detail) $ / shares in Units, $ in Thousands		1 Months Ended		3 Months Ended			9 Months Ended
	Sep. 29, 2019 shares	Aug. 31, 2015 $ / shares shares	Jul. 31, 2015 $ / shares shares	Sep. 30, 2019 USD ($) shares	Sep. 30, 2018 USD ($)	Mar. 31, 2018 USD ($) $ / shares shares	Sep. 30, 2019 USD ($) shares	Sep. 30, 2018 USD ($)	Dec. 31, 2013 $ / shares shares
Common Stock Warrants [Line Items]
Placement warrants not excercised and remained outstanding				2,156,153			2,156,153
Gain (loss) related to change in fair value | $							$ 4,674	$ 116
2018 Direct Registered Offering | Common Stock
Common Stock Warrants [Line Items]
Warrants issued						1,418,116
Exercise price | $ / shares						$ 8.31
Common stock warrants, expiration date						Mar. 31, 2025
Proceed from private placement and equity issuances, gross | $						$ 59,100
Fair value of warrants upon issuance | $						$ 7,400
Warrants, fair value measurement inputs						7 years
Allocated portion of proceeds from issuance of stock and warrants | $						$ 6,600
2018 Direct Registered Offering | Common Stock | Expected Volatility
Common Stock Warrants [Line Items]
Warrants, fair value measurement inputs						0.625
2018 Direct Registered Offering | Common Stock | Risk-free Interest Rate
Common Stock Warrants [Line Items]
Warrants, fair value measurement inputs						0.028
2018 Direct Registered Offering | Common Stock | Expected Dividend Yield
Common Stock Warrants [Line Items]
Warrants, fair value measurement inputs						0.00
Equity Classified Common Stock Warrants
Common Stock Warrants [Line Items]
Warrants issued									128,231
Exercise price | $ / shares									$ 5.84
Number of warrant exercised	128,231
Stock issued during period	36,457
Placement warrants not excercised and remained outstanding				0			0
2015 Placement Equity Classified Common Stock Warrants | Insiders
Common Stock Warrants [Line Items]
Warrants issued		198,760	198,760
Exercise price | $ / shares		$ 5.00	$ 5.00
Number of warrant exercised	159,010
Stock issued during period	92,487
Placement warrants not excercised and remained outstanding				39,750			39,750
Warrant expiration period		5 years	5 years
2016 and 2017 Placement Warrants | Common Stock
Common Stock Warrants [Line Items]
Gain (loss) related to change in fair value | $				$ 13,500	$ (6,700)		$ 8,600	$ 400