Stockholders' Equity (Details 3) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Summary of stock option exercise data
Number of options exercised (in shares)	210,256	460,600	807,755	1,177,797
Cash received	$ 8,574	$ 17,220	$ 33,019	$ 39,391