Summary of Operations and Significant Accounting Policies (Summary of Stock Option Activity and Weighted Average Exercise Prices) (Details) (USD $)	6 Months Ended
	Jun. 30, 2013
Options
Options outstanding at December 31, 2012	9,841,479
Options granted	676,300
Options exercised	(255,721)
Options cancelled	(917,841)
Options outstanding at June 30, 2013	9,344,217
Options exercisable at June 30,2013	4,015,798
Weighted Average Exercise Price
Options outstanding at December 31, 2013	$ 11.06
Options granted	$ 12.49
Options exercised	$ 6.34
Options cancelled	$ 13.37
Options outstanding at June 30, 2013	$ 11.07
Options exercisable at June 30,2013	$ 7.41