Overview and Basis of Presentation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended	6 Months Ended	62 Months Ended
	Jul. 02, 2019	Oct. 12, 2018	Nov. 30, 2018	Jun. 30, 2019	Jun. 30, 2019
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Proceeds from common stock offering				$ 7,912	$ 580,200
Proceeds from issuance of convertible preferred stock					85,000
Proceeds due from at-the-market offerings				27,140	27,140
Collaborative Arrangement [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Proceeds from common stock offering					$ 146,700
Sales Agreement [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Proceeds from common stock offering			$ 28,500	$ 35,200
Percentage of gross proceeds from common stock as sales agent cash commission		3.00%	3.00%	3.00%
Number of common stock issued upon conversion of shares			1,659,300	2,210,397
Common stock price per share			$ 18.00	$ 16.41	$ 16.41
Sales Agreement [Member] | General and Administrative Expenses [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Legal accounting and other fees			$ 400	$ 100
Sales Agreement [Member] | Maximum [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Proceeds from common stock offering		$ 100,000
Initial Public Offering and Concurrent Private Placements [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Proceeds from common stock offering					$ 170,500
Follow-on public Offering [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Proceeds from common stock offering					141,000
At-the-market Offering [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Proceeds from common stock offering					$ 37,000
At-the-market Offering [Member] | Subsequent Event [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Proceeds from common stock offering	$ 27,100