8. Stockholders’ Equity (Details) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Weighted average of the assumptions used to value stock options on the date of grant
Weighted average expected stock price volatility	86.90%	78.20%	85.40%	71.70%
Estimated dividend yield	0.00%	0.00%	0.00%	0.00%
Risk-free interest rate	1.90%	1.40%	2.10%	1.40%
Expected life of option (in years)	6 years 72 days	6 years 72 days	6 years 72 days	6 years 72 days
Weighted average grant date fair value per option	$ 3.09	$ 3.60	$ 2.12	$ 12.60