Common Stock, Common Stock Warrants and Stock Option Plan - Stock Options Outstanding and Vested (Details)	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Exercise Price $1.60 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Prices, Upper Limit (in dollars per share)	$ 1.60
Number of Stock Options Outstanding (in shares) | shares	11,759
Weighted Average Remaining Contractual Life (Years)	8 years 9 months 18 days
Weighted- Average Exercise Price per Share (in dollars per share)	$ 1.60
Shares Subject to Stock Options (in shares) | shares	6,424
Weighted Average Exercise Price Per Share (in dollars per share)	$ 1.60
Exercise Price $1.65 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Prices, Upper Limit (in dollars per share)	$ 1.65
Number of Stock Options Outstanding (in shares) | shares	398,988
Weighted Average Remaining Contractual Life (Years)	4 years 4 months 24 days
Weighted- Average Exercise Price per Share (in dollars per share)	$ 1.65
Shares Subject to Stock Options (in shares) | shares	383,572
Weighted Average Exercise Price Per Share (in dollars per share)	$ 1.65
Exercise Price $3.30 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Prices, Upper Limit (in dollars per share)	$ 3.30
Number of Stock Options Outstanding (in shares) | shares	115,984
Weighted Average Remaining Contractual Life (Years)	6 years 9 months 18 days
Weighted- Average Exercise Price per Share (in dollars per share)	$ 3.30
Shares Subject to Stock Options (in shares) | shares	115,913
Weighted Average Exercise Price Per Share (in dollars per share)	$ 3.30
Exercise Price $3.48 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Prices, Upper Limit (in dollars per share)	$ 3.48
Number of Stock Options Outstanding (in shares) | shares	170,238
Weighted Average Remaining Contractual Life (Years)	8 years
Weighted- Average Exercise Price per Share (in dollars per share)	$ 3.48
Shares Subject to Stock Options (in shares) | shares	114,715
Weighted Average Exercise Price Per Share (in dollars per share)	$ 3.48
Exercise Price $3.55 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Prices, Upper Limit (in dollars per share)	$ 3.55
Number of Stock Options Outstanding (in shares) | shares	370,275
Weighted Average Remaining Contractual Life (Years)	9 years 2 months 12 days
Weighted- Average Exercise Price per Share (in dollars per share)	$ 3.55
Shares Subject to Stock Options (in shares) | shares	58,578
Weighted Average Exercise Price Per Share (in dollars per share)	$ 3.55
Exercise Price $3.60 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Prices, Upper Limit (in dollars per share)	$ 3.60
Number of Stock Options Outstanding (in shares) | shares	132,100
Weighted Average Remaining Contractual Life (Years)	9 years 1 month 6 days
Weighted- Average Exercise Price per Share (in dollars per share)	$ 3.60
Shares Subject to Stock Options (in shares) | shares	32,407
Weighted Average Exercise Price Per Share (in dollars per share)	$ 3.60
Exercise Price $5.25 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Prices, Upper Limit (in dollars per share)	$ 5.25
Number of Stock Options Outstanding (in shares) | shares	281,852
Weighted Average Remaining Contractual Life (Years)	9 years 1 month 6 days
Weighted- Average Exercise Price per Share (in dollars per share)	$ 5.25
Shares Subject to Stock Options (in shares) | shares	45,273
Weighted Average Exercise Price Per Share (in dollars per share)	$ 5.25
Exercise Price $7.85 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Prices, Upper Limit (in dollars per share)	$ 7.85
Number of Stock Options Outstanding (in shares) | shares	25,500
Weighted Average Remaining Contractual Life (Years)	9 years 9 months 18 days
Weighted- Average Exercise Price per Share (in dollars per share)	$ 7.85
Exercise Price $10.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Prices, Upper Limit (in dollars per share)	$ 10.00
Number of Stock Options Outstanding (in shares) | shares	53,757
Weighted Average Remaining Contractual Life (Years)	7 years 9 months 18 days
Weighted- Average Exercise Price per Share (in dollars per share)	$ 10.00
Shares Subject to Stock Options (in shares) | shares	35,353
Weighted Average Exercise Price Per Share (in dollars per share)	$ 10.00
Exercise Price $0.99-$10.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Prices, Lower Limit (in dollars per share)	1.60
Exercise Prices, Upper Limit (in dollars per share)	$ 10.00
Number of Stock Options Outstanding (in shares) | shares	1,560,453
Weighted Average Remaining Contractual Life (Years)	7 years 7 months 6 days
Weighted- Average Exercise Price per Share (in dollars per share)	$ 3.63
Shares Subject to Stock Options (in shares) | shares	792,235
Weighted Average Exercise Price Per Share (in dollars per share)	$ 2.95