Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands				1 Months Ended		6 Months Ended	12 Months Ended
	Feb. 03, 2021	Jan. 21, 2020	Jul. 15, 2015	Aug. 31, 2020	May 31, 2020	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock shares reserved for issuance							16,386,314	18,577,117
Stock option grants description							The aggregate number of shares issued over the term of the 2015 Employee Stock Purchase Plan will not exceed 85,000 shares of common stock. The ESPP will not become effective until such time as the Compensation Committee determines in the future, and as of December 31, 2020, the initial offering periods had not commenced.
Total stock-based compensation							$ 9,470	$ 5,695	$ 6,796
2018 Equity Inducement Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock shares reserved for issuance							537,500			37,500
Common shares authorized to be issued during the period						500,000
Stock option life in years							10 years
2018 Equity Inducement Plan [Member] | Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares authorized to be issued during the period	500,000
2015 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock shares reserved for issuance							4,678,597
Common shares authorized to be issued during the period		4,312,500
Stock option life in years							10 years
Percentage threshold of outstanding shares increased annually under the plan							4.00%
Stock option grants description							the number of shares equal to 4% of the total outstanding shares of the Company’s common stock as of the immediately preceding December 31.
2008 Plan, 2015 Plan and 2018 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares authorized to be issued during the period							4,887,187
Weighted-average grant date fair values of options granted							$ 8.81	$ 50.40	$ 70.00
Issuance of common stock for exercise of stock options, Shares							0
Aggregate intrinsic value of options exercised								$ 100	$ 200
Total grant date fair value of options vested							$ 5,200	$ 6,000	$ 5,900
Total unrecognized stock-based compensation related to unvested stock options							$ 23,100
Weighted-average period							3 years 1 month 6 days
2008 Plan, 2015 Plan and 2018 Plan [Member] | Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Executives and employees stock options granted				1,107,250
Total stock-based compensation							$ 900
Total unrecognized stock-based compensation related to unvested stock options							8,900
2008 Plan, 2015 Plan and 2018 Plan [Member] | Share Based Compensation Arrangement Modification [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrant expiration period after specified event					75 days
Compensation costs relating to vesting acceleration and modification							$ 2,200
2015 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock shares reserved for issuance			17,500				17,500	17,500
Common shares authorized to be issued during the period			85,000
Number of common stock issued							0