Stockholders' Equity (Details 4) (Employee Stock Purchase Plan)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Employee Stock Purchase Plan
Summary of the Employee Stock Purchase Plan activity
Outstanding and exercisable, beginning of period	458,694	530,070	433,452	425,196
Granted	0	0	246,717	327,936
Exercised	(13,490)	(8,787)	(53,005)	(21,368)
Forfeited	(11,403)	(23,547)	(22,812)	(51,713)
Expired	0	0	(170,551)	(182,315)
Outstanding and exercisable, end of period	433,801	497,736	433,801	497,736