Stockholders' Equity (Summary of Stock Option Activity and Weighted Average Exercise Prices) (Details) (USD $)	9 Months Ended
	Sep. 30, 2013
Options
Options outstanding at December 31, 2012	9,841,479
Options granted	2,121,200
Options exercised	(446,107)
Options cancelled	(1,384,530)
Options outstanding at September 30, 2013	10,132,042
Options exercisable at September 30, 2013	4,451,913
Weighted Average Exercise Price
Options outstanding at December 31, 2012	$ 11.06
Options granted	$ 10.38
Options exercised	$ 5.94
Options cancelled	$ 13.05
Options outstanding at September 30, 2013	$ 10.87
Options exercisable at September 30, 2013	$ 8.54