Fair Value Measurements - Summary of Common Stock Warrant Liability and Derivative Liability Assumptions (Detail) - $ / shares		9 Months Ended	12 Months Ended
	Mar. 15, 2017	Sep. 30, 2017	Dec. 31, 2016
Private Placement Common Stock Warrant Liability [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Stock Price		$ 3.70	$ 2.70
Exercise Price		$ 1.12	$ 4.00
Remaining term (in years)		5 years 6 months 14 days	6 years 3 months 15 days
Volatility		62.00%	51.40%
Risk-free interest rate		1.98%	2.14%
Placement Agent Common Stock Warrant Liability [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Stock Price		$ 3.70	$ 2.70
Exercise Price		$ 1.12	$ 3.99
Remaining term (in years)		3 years 6 months 15 days	4 years 3 months 15 days
Volatility		76.00%	56.10%
Risk-free interest rate		1.69%	1.77%
JGB Common Stock Warrant Liability [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Stock Price	$ 2.15	$ 3.70
Exercise Price	$ 5.00	$ 4.82
Remaining term (in years)	5 years 6 months	4 years 11 months 16 days
Volatility	54.00%	65.00%
Risk-free interest rate	2.06%	1.90%
Majority Shareholder Common Stock Warrant Liability [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Stock Price		$ 3.70	$ 2.70
Exercise Price		$ 4.00	$ 4.00
Remaining term (in years)		5 years 8 months 16 days	6 years 3 months 15 days
Volatility		62.00%	51.40%
Risk-free interest rate		1.99%	2.14%
Derivative Liability [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Stock Price	$ 2.15	$ 3.70
Remaining term (in years)	2 years 11 months 15 days	2 years 4 months 28 days
Volatility	54.00%	65.00%
Risk-free interest rate	1.72%	1.90%