Stockholders' Equity (Summary of Stock Option Activity and Weighted Average Exercise Prices) (Details) (USD $)	3 Months Ended
	Mar. 31, 2014
Options
Options outstanding at December 31, 2013	9,724,193
Options granted	563,500
Options exercised	(222,083)
Options cancelled	(387,028)
Options outstanding at March 31, 2014	9,678,582
Options exercisable at March 31, 2014	4,205,765
Weighted Average Exercise Price
Options outstanding at December 31, 2013	$ 10.86
Options granted	$ 13.22
Options exercised	$ 9.17
Options cancelled	$ 14.25
Options outstanding at March 31, 2014	$ 10.90
Options exercisable at March 31, 2014	$ 8.94