Common Stock and Preferred Stock - Additional Information (Detail) $ / shares in Units, $ in Thousands	1 Months Ended				12 Months Ended
	Jul. 31, 2018 USD ($) shares	Jan. 31, 2018 USD ($)	Jun. 30, 2017 USD ($) shares	May 31, 2015 USD ($)	Dec. 31, 2018 USD ($) Vote $ / shares shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares
Subsidiary, Sale of Stock [Line Items]
Proceeds from sale of common stock, net | $					$ 53,829	$ 56,486	$ 26,223
Proceeds from underwritten public offering after fees and commissions | $			$ 56,500
Sale of Stock, Number of Shares Issued in Transaction			3,450,000
Subsidiary or Equity Method Investee, Cumulative Proceeds Received on All Transactions | $			$ 57,800
Each share of common stock is entitled to vote | Vote					1
Preferred stock, shares authorized (in shares)					15,000,000	15,000,000
Preferred stock, shares issued (in shares)					0	0
Preferred stock, shares outstanding (in shares)					0
Preferred stock warrants were converted into warrants to purchase common stock (in shares)					905,798
Exercise price of common stock warrants (in dollars per share) | $ / shares					$ 18.38
Overallotment option
Subsidiary, Sale of Stock [Line Items]
Sale of Stock, Number of Shares Issued in Transaction	600,000		450,000
At the market equity offering
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued (in shares)							1,331,539	960,400
Proceeds from sale of common stock, net | $		$ 40,000		$ 40,000
Commission Expense, Percentage		3.00%
Proceeds from underwritten public offering after fees and commissions | $							$ 26,100	$ 12,500
Public Stock Offering [Member]
Subsidiary, Sale of Stock [Line Items]
Proceeds from underwritten public offering after fees and commissions | $	$ 53,800
Sale of Stock, Number of Shares Issued in Transaction	4,600,000
Sale Of Stock, Gross Consideration Received On Transaction | $	$ 57,500