Common Stock (Stock Option Activity and Additional Details) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted	0	0	0
Shares
Outstanding as of January 1, 2014	1,864,042
Exercised	(311,954)	(571,500)
Forfeited	(7,128)
Expired	0
Outstanding as of December 31, 2014	1,544,960	1,864,042
Vested or expected to vest at December 31, 2014	1,544,960
Options exercisable as of December 31, 2014	1,544,960
Weighted-Average Exercise Price (in dollars per share)
Outstanding as of January 1, 2014	$ 4.95
Exercised	$ 5.32
Forfeited	$ 17.58
Expired	$ 0.00
Outstanding as of December 31, 2014	$ 4.81	$ 4.95
Vested or expected to vest at December 31, 2014	$ 4.81
Options exercisable as of December 31, 2014	$ 4.81
Weighted Average Remaining Conctracual Term (in years)
Outstanding as of December 31, 2014	1 year 9 months 22 days
Vesting or expected to vest at December 31, 2014	1 year 9 months 22 days
Options exercisable as of December 31, 2014	1 year 9 months 22 days
Aggregate Intrinsic Value
Outstanding as of December 31, 2014	$ 21,497,484
Vesting or expected to vest at December 31, 2014	21,497,484
Options exercisable as of December 31, 2014	21,497,484
Stock Options, Additional Disclosures
Total intrinsic value of stock options exercised	6,000,000	5,600,000	600,000
Total fair value of stock options vesting (less than $0.1 million in 2014)	$ 100,000	$ 4,200,000	$ 500,000
Stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award expiration period	10 years
Vesting period in years	4 years