Stockholders' Equity (Details 3) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Number of Shares
Balance at the beginning of the period (in shares)	1,820,784
Options granted (in shares)	1,298,500
Options exercised (in shares)	(56,418)
Balance at the end of the period (in shares)	2,677,774	1,820,784
Options vested and expected to vest at the end of the period (in shares)	2,407,005
Options exercisable (in shares)	1,172,747
Weighted-Average Exercise Price (Per Share)
Balance at the beginning of the period (in dollars per share)	$ 4.46
Options granted (in dollars per share)	$ 4.24
Options forfeited (in dollars per share)	$ 5.81
Options exercised (in dollars per share)	$ 1.17
Balance at the ending of the period (in dollars per share)	$ 4.24	$ 4.46
Options vested and expected to vest at the end of the period (in dollars per share)	$ 4.22
Options exercisable (in dollars per share)	$ 3.93
Weighted-average fair value of options granted during the period	$ 2.73	$ 3.03	$ 6.98
Weighted-Average Remaining Contractual Term (in years)
Balance at the end of the period	5 years 7 months 6 days
Options vested and expected to vest at the end of the period	5 years 6 months 22 days
Options exercisable	5 years 18 days
Aggregate Intrinsic Value (in thousands)
Balance at the end of the period	$ 239
Options vested and expected to vest at the end of the period	234
Options exercisable	$ 215
Stock option activity
Options canceled (in shares)	258,969