Notes Payable and Stock Purchase Warrants - Term Notes Payable (Details)	1 Months Ended	3 Months Ended
	Jul. 31, 2019 USD ($) $ / shares	Mar. 31, 2018 USD ($) $ / shares	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
2023 Notes
Long term debt
Principal amount		$ 53,000,000	$ 15,700,000	$ 15,700,000
Conversion rate (per $1,000 of principal)		294.1176
Amount of principal which is converted to shares		$ 1,000
Conversion price (in dollars per share) | $ / shares		$ 3.40
Repurchase amount	$ 37,000,000
2025 Notes
Long term debt
Principal amount	$ 82,000,000		$ 82,000,000	$ 82,000,000
Conversion rate (per $1,000 of principal)	757.5758
Amount of principal which is converted to shares	$ 1,000
Conversion price (in dollars per share) | $ / shares	$ 1.32