Fair Value Measurements and Fair Value of Financial Instruments - Summary of Cash Equivalents and Short-term Investments (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	$ 166,940	$ 100,117
Unrealized Gains	103	28
Unrealized Losses	(139)	(7)
Estimated Fair Value	166,904	100,138
Less: Cash Equivalents, Amortized Cost Basis	(119,540)	(51,391)
Less: Cash equivalents, unrealized gains	15	0
Less: Cash equivalents, unrealized losses	(15)	(3)
Less: Cash Equivalents, Estimated Fair Value	(119,540)	(51,388)
Money market funds | Quoted Prices in Active Markets (Level 1)
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	18,315	15,056
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated Fair Value	18,315	15,056
U.S. government and agency securities | Significant Other Observable Inputs (Level 2)
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	86,930	37,974
Unrealized Gains	78	14
Unrealized Losses	(3)	(2)
Estimated Fair Value	87,005	37,986
Commercial paper | Significant Other Observable Inputs (Level 2)
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	171,736	87,983
Unrealized Gains	9	8
Unrealized Losses	(121)	(8)
Estimated Fair Value	171,624	87,983
Corporate Bonds | Significant Other Observable Inputs (Level 2)
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	9,499	10,495
Unrealized Gains	1	6
Unrealized Losses	0	0
Estimated Fair Value	9,500	10,501
Total Cash Equivalents and Short-term Investments
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	286,480	151,508
Unrealized Gains	88	28
Unrealized Losses	(124)	(10)
Estimated Fair Value	$ 286,444	$ 151,526