Stockholders' Equity (Details 4) (Employee Stock Purchase Plan [Member])	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Employee Stock Purchase Plan [Member]
Summary of the Employee Stock Purchase Plan activity
Outstanding and exercisable, beginning of period	433,452	425,196
Granted	246,717	327,936
Exercised	(39,515)	(12,581)
Forfeited	(11,409)	(28,166)
Expired	(170,551)	(182,315)
Outstanding and exercisable, end of period	458,694	530,070