Stockholders' Equity - Summary of activity under Employee Stock Purchase Plan (Details) (Employee Stock Purchase Plan, USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Summary of the Employee Stock Purchase Plan activity
Outstanding and exercisable, beginning of period	391,108	433,452
Granted	275,655	246,717
Exercised	(18,502)	(39,515)
Forfeited	(22,426)	(11,409)
Expired	(157,875)	(170,551)
Outstanding and exercisable, end of period	467,960	458,694
Option to purchase to common stock	$ 25,000
Discount on market price on the date of grant	85.00%
Discount on market price on the date of exercise	85.00%
Award expiration date	27 months
General and Administrative Expense
Summary of the Employee Stock Purchase Plan activity
Share-based compensation expense	$ 200,000