Stockholders' Equity - Issuance of Common Stock and Warrants (Details)			1 Months Ended	3 Months Ended	6 Months Ended
	Jun. 21, 2019 $ / shares shares	May 29, 2018 $ / shares shares	May 31, 2018 USD ($) $ / shares shares	Jun. 30, 2019 USD ($) $ / shares	Jun. 30, 2019 USD ($) $ / shares	Jul. 01, 2018 USD ($)	Mar. 29, 2019 USD ($) offering	Dec. 30, 2018 $ / shares
Class Of Stock [Line Items]
Common stock, par value (in dollars per share) | $ / shares	$ 0.001			$ 0.001	$ 0.001			$ 0.001
Shares issued price per share (in dollars per share) | $ / shares	$ 0.50
Net proceeds from issuance of common stock | $			$ 13,900,000	$ 8,300,000	$ 9,439,000	$ 15,855,000
Shelf registration, number of offerings | offering							1
Shelf registration, maximum offering | $							$ 75,000,000
Number of common stock contain in each unit			1
Number of warrant contain in each unit			0.40
Exercise price of each unit | $ / shares			$ 1.15
Exercisable period of warrants		60 months
Strike price of warrants (in dollars per share) | $ / shares		$ 1.38
Fair value assumptions of warrants, expected term		5 years
Measurement Input, Share Price
Class Of Stock [Line Items]
Warrants and Rights Outstanding, Measurement Input		0.57
Measurement Input, Risk Free Interest Rate
Class Of Stock [Line Items]
Warrants and Rights Outstanding, Measurement Input		2.58
Measurement Input, Price Volatility
Class Of Stock [Line Items]
Warrants and Rights Outstanding, Measurement Input		52.75
Measurement Input, Expected Dividend Rate
Class Of Stock [Line Items]
Warrants and Rights Outstanding, Measurement Input		0
Common stock
Class Of Stock [Line Items]
Aggregate shares of common stock issued	18,400,000		13,500,000
Common stock | Maximum
Class Of Stock [Line Items]
Warrants to purchase aggregate shares of common stock		5,400,000	5,400,000
Exercise of Option for Overallotment of Shares by Underwriters | Common stock
Class Of Stock [Line Items]
Aggregate shares of common stock issued	2,400,000