Fair Value Measurements - Valuation Technique (Details) $ in Millions		12 Months Ended
	Jan. 01, 2019	Dec. 31, 2018	Dec. 31, 2019 USD ($)
$40M Convertible Senior Note
Valuation technique for assets and liabilities measured and recorded at fair value
Fair value of convertible senior notes			$ 53.5
$100M Convertible Senior Notes
Valuation technique for assets and liabilities measured and recorded at fair value
Fair value of convertible senior notes			$ 135.3
Volatility | $40M Convertible Senior Note | Level 3
Valuation technique for assets and liabilities measured and recorded at fair value
Debt Instrument, Measurement Input			70
Derivative Liabilities | Expected dividend yield
Valuation technique for assets and liabilities measured and recorded at fair value
Derivative Liability, Measurement Input			0
Minimum | Warrants | Risk free interest rate
Valuation technique for assets and liabilities measured and recorded at fair value
Equity Instrument, Measurement Input	2.60
Minimum | Warrants | Volatility
Valuation technique for assets and liabilities measured and recorded at fair value
Equity Instrument, Measurement Input		75.00
Minimum | Derivative Liabilities | Risk free interest rate
Valuation technique for assets and liabilities measured and recorded at fair value
Derivative Liability, Measurement Input		1.64
Minimum | Derivative Liabilities | Volatility
Valuation technique for assets and liabilities measured and recorded at fair value
Derivative Liability, Measurement Input		18.40
Minimum | Derivative Liabilities | Expected average term
Valuation technique for assets and liabilities measured and recorded at fair value
Derivative Liability, Expected average term		4 days
Minimum | Warrants | Risk free interest rate
Valuation technique for assets and liabilities measured and recorded at fair value
Equity Instrument, Measurement Input		2.60
Minimum | Warrants | Expected average term
Valuation technique for assets and liabilities measured and recorded at fair value
Equity Instrument Expected average term	8 years 3 months 4 days	8 years 3 months 4 days
Maximum | Warrants | Risk free interest rate
Valuation technique for assets and liabilities measured and recorded at fair value
Equity Instrument, Measurement Input	2.63
Maximum | Warrants | Volatility
Valuation technique for assets and liabilities measured and recorded at fair value
Equity Instrument, Measurement Input		85.00
Maximum | Warrants | Expected average term
Valuation technique for assets and liabilities measured and recorded at fair value
Equity Instrument Expected average term	8 years 6 months 18 days
Maximum | Derivative Liabilities | Risk free interest rate
Valuation technique for assets and liabilities measured and recorded at fair value
Derivative Liability, Measurement Input		2.66
Maximum | Derivative Liabilities | Volatility
Valuation technique for assets and liabilities measured and recorded at fair value
Derivative Liability, Measurement Input		81.69
Maximum | Derivative Liabilities | Expected average term
Valuation technique for assets and liabilities measured and recorded at fair value
Derivative Liability, Expected average term		1 year 6 months 11 days
Maximum | Warrants | Risk free interest rate
Valuation technique for assets and liabilities measured and recorded at fair value
Equity Instrument, Measurement Input		3.02
Maximum | Warrants | Expected average term
Valuation technique for assets and liabilities measured and recorded at fair value
Equity Instrument Expected average term		9 years 3 months 18 days
Weighted Average | Warrants | Volatility
Valuation technique for assets and liabilities measured and recorded at fair value
Equity Instrument, Measurement Input	0.95