Common Stock (Stock Option Activity) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Shares
Outstanding as of January 1, 2012	2,529,690
Exercised	(67,500)	(64,232)
Expired	(4,604)
Outstanding as of December 31, 2012	2,457,586	2,529,690
Vested or expected to vest at December 31, 2012	2,437,864
Options exercisable as of December 31, 2012	1,318,436
Weighted-Average Exercise Price
Outstanding as of January 1, 2012	$ 5.32
Exercised	$ 2.50
Expired	$ 13.81
Outstanding as of December 31, 2012	$ 5.65	$ 5.32
Vested or expected to vest at December 31, 2012	$ 5.64
Options exercisable as of December 31, 2012	$ 3.56
Weighted Average Remaining Conctracual Term (in years)
Outstanding as of December 31, 2012	7 years 1 month 21 days
Vesting or expected to vest at December 31, 2012	7 years 1 month 21 days
Options exercisable as of December 31, 2012	6 years 6 months 29 days
Aggregate Intrinsic Value
Outstanding as of December 31, 2012	$ 16,673,502
Vesting or expected to vest at December 31, 2012	16,571,402
Options exercisable as of December 31, 2012	11,728,379
Stock Options, Additional Disclosures
Weighted-average fair value of stock options at grant-date		$ 8.47	$ 2.06
Total intrinsic value of stock options exercised	600,000	200,000	100,000
Total fair value of stock options vesting	500,000	500,000	800,000
Stock options [Member]
Stock Options, Additional Disclosures
Unrecognized compensation expense related to non-vested stock options	$ 1,000,000
Weighted-average period unrecognized compensation expense is expected to be recognized	4 months 24 days