Stockholders' Equity - Additional Information (Detail) - USD ($)				1 Months Ended		3 Months Ended				9 Months Ended
	Aug. 20, 2019	Jul. 29, 2019	Mar. 20, 2019	Jul. 31, 2019	May 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Apr. 04, 2019	Dec. 31, 2018
Subsidiary Sale Of Stock [Line Items]
Restricted stock units vested shares					74,166
Common stock, shares issued					74,166	46,673,977				46,673,977			39,547,558
Unregistered common stock exchanged for consulting services								$ 197,000		$ 197,000
Compensation expense						$ 2,713,000			$ 1,819,000	7,628,000	$ 5,759,000
Shareholder Consulting Agreement [Member]
Subsidiary Sale Of Stock [Line Items]
Price per share			$ 19.37
Number of shares of unregistered common stock exchanged for consulting services			10,195
Consulting services performance period			6 months
General and Administrative [Member]
Subsidiary Sale Of Stock [Line Items]
Compensation expense						1,322,000			$ 918,000	3,829,000	$ 3,358,000
General and Administrative [Member] | Shareholder Consulting Agreement [Member]
Subsidiary Sale Of Stock [Line Items]
Compensation expense						$ 98,000				$ 197,000
Non-Exclusive License Agreement
Subsidiary Sale Of Stock [Line Items]
Upfront fee	$ 8,000,000
Upfront fee payable, cash	4,000,000
Upfront fee payable, stock	$ 4,000,000
Price per share	$ 23.42
Share price average, Determination period	30 days
Percentage of payment, stock	50.00%
Maximum [Member]
Subsidiary Sale Of Stock [Line Items]
Aggregate offering price of securities												$ 300,000,000
Common Stock [Member]
Subsidiary Sale Of Stock [Line Items]
Common stock, shares issued				6,325,000
Restricted stock units vested shares					74,166		74,166
Number of shares of unregistered common stock exchanged for consulting services								10,195
Common Stock [Member] | Non-Exclusive License Agreement
Subsidiary Sale Of Stock [Line Items]
Common stock, shares issued	170,793
Upfront fee payable, stock	$ 4,000,000
Common Stock [Member] | Follow-on Public Offering [Member]
Subsidiary Sale Of Stock [Line Items]
Common stock, shares issued						6,325,000			5,175,000
Price per share				$ 23.00		$ 23			$ 19	$ 23	$ 19
Common Stock [Member] | Underwriter's Over-Allotment [Member]
Subsidiary Sale Of Stock [Line Items]
Common stock, shares issued		825,000		825,000
Proceeds from issuance of common stock net of underwriting discounts, commissions and estimated offering expenses		$ 136,525,000
Underwriting discounts, commission and estimated offering expenses		$ 8,950,000