Common Stock (Stock Option Activity and Additional Details) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Shares
Outstanding as of January 1, 2013	2,457,586
Exercised	(571,500)	(67,500)
Forfeited	(5,000)
Expired	(17,044)
Outstanding as of December 31, 2013	1,864,042	2,457,586
Vested or expected to vest at December 31, 2013	1,862,960
Options exercisable as of December 31, 2013	1,836,942
Weighted-Average Exercise Price
Outstanding as of January 1, 2013	$ 5.65
Exercised	$ 7.70
Forfeited	$ 1.38
Expired	$ 22.40
Outstanding as of December 31, 2013	$ 4.95	$ 5.65
Vested or expected to vest at December 31, 2013	$ 4.95
Options exercisable as of December 31, 2013	$ 4.98
Weighted Average Remaining Conctracual Term (in years)
Outstanding as of December 31, 2013	6 years 3 months 4 days
Vesting or expected to vest at December 31, 2013	6 years 3 months 4 days
Options exercisable as of December 31, 2013	6 years 3 months 1 day
Aggregate Intrinsic Value
Outstanding as of December 31, 2013	$ 28,253,321
Vesting or expected to vest at December 31, 2013	28,216,770
Options exercisable as of December 31, 2013	27,763,907
Stock Options, Additional Disclosures
Total intrinsic value of stock options exercised	5,600,000	600,000	200,000
Total fair value of stock options vesting	4,200,000	500,000	500,000
Unrecognized compensation expense related to non-vested stock options	$ 100,000
Stock options [Member]
Stock Options, Additional Disclosures
Award expiration period	10 years
Vesting period in years	4 years
Award unrecognized compensation expense, expected period for recognition	10 months 24 days