Stockholders' Equity - Summary of activity under Employee Stock Purchase Plan (Details) - Employee Stock Purchase Plan [Member] - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Summary of the Employee Stock Purchase Plan activity
Outstanding and exercisable, beginning of period (shares)	344,908	365,219	340,958	393,902
Granted (shares)	0	0	198,450	197,640
Exercised (shares)	(13,947)	(3,883)	(51,475)	(39,814)
Forfeited (shares)	(3,561)	(9,807)	(17,451)	(41,253)
Expired (shares)	0	0	(143,082)	(158,946)
Outstanding and exercisable, end of period (shares)	327,400	351,529	327,400	351,529