Subsequent Events - Additional Information (Detail) $ / shares in Units, $ in Millions				3 Months Ended
	Jul. 22, 2019 USD ($) $ / shares shares	Jul. 05, 2019 USD ($)	Jul. 02, 2019 shares	Jun. 30, 2019 shares	Mar. 31, 2019 shares	Jun. 30, 2018 shares	Mar. 31, 2018 shares	Dec. 31, 2018 shares
Subsequent Event [Line Items]
Common stock, shares authorized				147,500,000				135,000,000
Convertible Preferred Stock
Subsequent Event [Line Items]
Convertible preferred stock, share outstanding				112,500,000				100,000,000
Common Stock
Subsequent Event [Line Items]
Issuance of common stock, Shares				148,320	134,013	187,421	125,123
Subsequent Event
Subsequent Event [Line Items]
Reverse stock split		one-for-seven
Stock split		0.14285
Gross proceeds threshold of automatic conversion of preferred stock eliminated | $		$ 45.0
Common stock, shares authorized	200,000,000
Preferred stock authorized	10,000,000
Subsequent Event | 2019 Employee Stock Purchase Plan
Subsequent Event [Line Items]
Shares reserved for future issuance			252,142
Increase in number of shares reserved for issuance (shares)			428,571
Increase in number of shares reserved for issuance, percent of common stock outstanding			1.00%
Subsequent Event | IPO
Subsequent Event [Line Items]
Issuance of common stock, Shares	4,500,000
Shares issued, price per share | $ / shares	$ 16.00
Net proceeds of common stock | $	$ 63.9
Subsequent Event | IPO | Common Stock
Subsequent Event [Line Items]
Number of preferred stock converted into common stock	16,071,418
Subsequent Event | 2019 Stock Incentive Plan
Subsequent Event [Line Items]
Shares reserved for future issuance			2,017,142
Increase in number of shares reserved for issuance (shares)			2,000,000
Increase in number of shares reserved for issuance, percent of common stock outstanding			4.00%