Stockholders' Equity, Stock Option (Details) (Stock Options [Member], USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Stock Options [Member]
Stock option activity [Roll Forward]
Outstanding options, beginning balance (in shares)	9,529,597
Granted (in shares)	97,400
Exercised (in shares)	(1,327,850)
Forfeited (in shares)	(52,771)
Outstanding options, ending balance (in shares)	8,246,376		9,529,597
Options vested and expected to vest (in shares)	8,179,531
Exercisable options (in shares)	6,027,022
Options Outstanding, Weighted Average Exercise Price [Roll Forward]
Options outstanding, weighted average exercise price, beginning balance (in dollars per share)	$ 3.05
Granted, weighted average exercise price (in dollars per share)	$ 4.17
Exercised, weighted average exercise price (in dollars per share)	$ 2.33
Forfeited, weighted average exercise price (in dollars per share)	$ 4.90
Options outstanding, weighted average exercise price, ending balance (in dollars per share)	$ 3.17		$ 3.05
Vested and expected to vest, Weighted Average Exercise Price (in dollars per share)	$ 3.16
Exercisable, weighted average exercise price (in dollars per share)	$ 3.07
Additional Disclosures [Abstract]
Options outstanding, Average Remaining Contractual Term	3 years 10 months 10 days		3 years 7 months 17 days
Vested and expected to vest, Average Remaining Contractual Term	3 years 10 months 2 days
Options exercisable, Average Remaining Contractual Term	3 years 2 months 26 days
Options outstanding, Aggregate Intrinsic Value	$ 10,204,000		$ 12,595,000
Vested and expected to vest, Aggregate Intrinsic Value	10,154,000
Options exercisable, Aggregate Intrinsic Value	7,743,000
Options exercised in period, total intrinsic value	2,400,000	89,000
Fair value of options vested	471,000	1,000,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized [Abstract]
Unrecognized compensation cost related to stock options	$ 2,600,000
Nonvested awards, unrecognized cost, period for recognition	1 year 8 months 12 days