Fair Value Measurements and Available for Sale Investments - Fair Value Assumptions (Details) - Derivative Financial Instruments, Liabilities - Fair Value, Measurements, Recurring - Series C Preferred Stock - $ / shares		12 Months Ended
	Jan. 31, 2017	Dec. 31, 2016
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value of preferred stock (in dollars per share)	$ 16.95	$ 12.67
Exercise price (in dollars per share)	$ 4.55	$ 4.55
Risk-free interest rate (as a percent)	1.40%	1.50%
Volatility (as a percent)	88.80%	88.60%
Dividend Yield (as a percent)	0.00%	0.00%
Contractual term (in years)	3 years 9 months	3 years 9 months 30 days
Weighted-average measurement date fair value per share (in dollars per share)	$ 13.71	$ 9.65