Formation and Business of the Company - Additional Information (Detail) - USD ($)	1 Months Ended		3 Months Ended		12 Months Ended
	Apr. 30, 2020	Jun. 30, 2016	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Formation and Business of the Company [Line Items]
Net loss			$ 24,888,000	$ 44,076,000	$ 103,700,000
Cash used in operations			5,181,000	$ 21,707,000	50,200,000
Accumulated deficit			$ 434,656,000		$ 409,768,000
1.75% Convertible Senior Notes due 2021 [Member]
Formation and Business of the Company [Line Items]
Debt instrument due year		2021	2021		2021
Aggregate principal amount of convertible senior notes		$ 150,000,000.0
Net proceeds from the debt offering after deducting transaction costs		$ 166,200,000
Subsequent Event [Member]
Formation and Business of the Company [Line Items]
Common stock in underwriting public offering	1,868,750
Net proceeds from common stock	$ 147,200,000
Subsequent Event [Member] | 2.75% Convertible senior notes due 2025 [Member]
Formation and Business of the Company [Line Items]
Aggregate principal amount of convertible senior notes	189,800,000
Net proceeds from the debt offering after deducting transaction costs	$ 183,700,000