Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended
	Sep. 30, 2016	Jun. 30, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Common stock, shares issued		16,898,664	15,413,610
Transfers of assets out of Level 1 into Level 2		$ 0
Transfers of assets out of Level 2 into Level 1		0
Transfers of liabilities out of Level 1 into Level 2		0
Transfers of liabilities out of Level 2 into Level 1		0
Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets		0
Liabilities		0
Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets		0
Liabilities		$ 0
2016 Financings [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Common stock, shares issued	5,048,632
Aggregate gross proceeds from sale of common stock and warrants	$ 14,500,000
2016 Financings [Member] | Maximum [Member] | Common Stock Warrants [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Warrants to purchase of common stock	2,975,444
Underwriters [Member] | Maximum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Warrants to purchase of common stock	252,432