Stockholders' Equity - Summary of Reserved Shares of Common Stock for Future Issuance (Parenthetical) (Details) - shares	Jan. 01, 2020	Jun. 06, 2019	Jan. 01, 2019	Dec. 12, 2018	Feb. 28, 2018	Jan. 01, 2018	Feb. 28, 2017	Mar. 31, 2020	Dec. 31, 2019	Jan. 30, 2019	Feb. 28, 2016	Feb. 28, 2014
Class of Stock [Line Items]
Common stock, shares reserved for future issuance								24,958,932	21,403,890
Shares Available for Issuance Under the ESPP
Class of Stock [Line Items]
Increase in common stock, shares reserved for future issuance		5,200,000			0		0
Common stock, shares reserved for future issuance								5,600,968	5,715,992
Maximum aggregate number of shares available for purchase											739,611
2014 Plans
Class of Stock [Line Items]
Increase in common stock, shares reserved for future issuance	4,031,376		3,801,198	2,323,213		1,575,329
Common stock, shares reserved for future issuance												1,785,000
Inducement Award Program
Class of Stock [Line Items]
Common stock, shares reserved for future issuance										3,150,000