Subsequent Events - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Apr. 30, 2019	Dec. 31, 2017
Amended Loan Agreement [Member]
Subsequent Event [Line Items]
Maturity date		Apr. 01, 2020
Subsequent Event [Member] | Term Loan Agreement [Member] | Silicon Valley Bank [Member]
Subsequent Event [Line Items]
Borrowing amount	$ 5,500,000
Debt instrument, payment terms	Under the terms of the SVB Loan Agreement, the Company is required to make interest-only payments through December 31, 2020 on the borrowings at a floating rate equal to the greater of the Prime Rate minus 2.25%, as defined in the SVB Loan Agreement, or 3.25%, followed by an amortization period of 24 months of equal monthly payments of principal plus interest amounts until paid in full.
Debt instrument, frequency of periodic payment	monthly
Maturity date	Dec. 01, 2022
Debt instrument, interest-only payments date	Dec. 31, 2020
Debt instrument, stated interest rate	3.25%
Debt instrument, amortization period	24 months
Final payment fee, percentage	4.00%
Subsequent Event [Member] | Term Loan Agreement [Member] | Silicon Valley Bank [Member] | Prime Rate [Member]
Subsequent Event [Line Items]
Debt instrument, basis spread on floating rate	2.25%
Subsequent Event [Member] | Term Loan Agreement [Member] | Silicon Valley Bank [Member] | Prior to 1st Anniversary of April 26, 2019, or Effective Date [Member]
Subsequent Event [Line Items]
Prepayment fee	$ 165,000
Subsequent Event [Member] | Term Loan Agreement [Member] | Silicon Valley Bank [Member] | After 1st Anniversary but Prior to 2nd Anniversary of Effective Date [Member]
Subsequent Event [Line Items]
Prepayment fee	110,000
Subsequent Event [Member] | Term Loan Agreement [Member] | Silicon Valley Bank [Member] | After 2nd Anniversary of Effective Date [Member]
Subsequent Event [Line Items]
Prepayment fee	55,000
Subsequent Event [Member] | Amended Loan Agreement [Member]
Subsequent Event [Line Items]
Repayment of remaining obligations	$ 5,900,000
Subsequent Event [Member] | Common Stock [Member]
Subsequent Event [Line Items]
Common stock, shares issued upon conversion of convertible preferred stock	4,950,165
Series B Convertible Preferred Stock [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Numbers of shares converted	13,639
Shares outstanding	0
Series C Convertible Preferred Stock [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Numbers of shares converted	1,558
Shares outstanding	0
Series D Convertible Preferred Stock [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Numbers of shares converted	1,119
Shares outstanding	1,381
Series E Stock [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Shares outstanding	10,000