Common Stock, Common Stock Warrants and Stock Option Plan - Stock Reserved for Future Issuance (Details) - shares	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2015
Class of Stock [Line Items]
Common stock, capital shares reserved for future issuance (in shares)	15,035,095	14,093,625
Convertible Notes Payable [Member]
Class of Stock [Line Items]
Common stock, capital shares reserved for future issuance (in shares)	8,885,204	8,885,204
Share-based Payment Arrangement, Option [Member]
Class of Stock [Line Items]
Common stock, capital shares reserved for future issuance (in shares)	1,626,244	1,929,391
Restricted Stock Units (RSUs) [Member]
Class of Stock [Line Items]
Common stock, capital shares reserved for future issuance (in shares)	2,253,181	1,451,507
Shares available for future grants (in shares)	557,671	288,813
Employee Stock [Member]
Class of Stock [Line Items]
Common stock, capital shares reserved for future issuance (in shares)	547,513	373,428	150,000
Common Stock Warrants [Member]
Class of Stock [Line Items]
Warrants to purchase common stock (in shares)	1,165,282	1,165,282