Stockholders' Equity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Shares
Granted	385,330
Weighted Average Remaining Contractual Term
Vested and expected to vest	5 years 9 months 18 days	5 years 8 months 12 days	6 years 1 month 6 days
Employee Stock Option [Member]
Shares
Outstanding, Beginning balance	4,191,004	7,389,894	5,974,039
Granted	200,000	369,814	2,547,585
Exercised	(2,492,639)	(778,783)	(352,718)
Forfeited	(166,000)	(2,712,613)	(635,424)
Expired	(12,336)	(77,308)	(143,588)
Outstanding, Ending balance	1,720,029	4,191,004	7,389,894	5,974,039
Exercisable, December 31, 2016	1,348,842
Vested and expected to vest, December 31, 2016	1,675,487
Weighted-Average Exercise Price
Outstanding, beginning balance	$ 2.36	$ 2.31	$ 2.52
Granted	2.20	1.66	1.81
Exercised	1.70	1.25	1.29
Forfeited	1.69	2.43	2.61
Expired	3.80	3.26	3.04
Outstanding, ending balance	3.36	$ 2.36	$ 2.31	$ 2.52
Exercisable, December 31, 2016	3.80
Vested and expected to vest, December 31, 2016	$ 3.40
Weighted Average Remaining Contractual Term
Outstanding	4 years 2 months 12 days	6 years	6 years 10 months 24 days	6 years 6 months
Exercisable	3 years 2 months 12 days
Vested and expected to vest	4 years 1 month 6 days