Stockholders' Equity, Stock Option (Details) (Stock Options [Member], USD $) In Thousands, except Share data, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Stock Options [Member]
Stock option activity [Roll Forward]
Outstanding options, beginning balance (in shares)	9,529,597
Granted (in shares)	256,550
Exercised (in shares)	(3,771,188)
Forfeited (in shares)	(216,049)
Outstanding options, ending balance (in shares)	5,798,910	9,529,597
Options vested and expected to vest (in shares)	5,742,681
Exercisable options (in shares)	4,541,237
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)	$ 4.37
Exercised, weighted average exercise price (in dollars per share)	$ 2.53
Forfeited, weighted average exercise price (in dollars per share)	$ 4.33
Options outstanding, weighted average exercise price, ending balance (in dollars per share)	$ 3.40	$ 3.05
Vested and expected to vest, Weighted Average Exercise Price (in dollars per share)	$ 3.40
Exercisable, weighted average exercise price (in dollars per share)	$ 3.23
Additional Disclosures [Abstract]
Options outstanding, Average Remaining Contractual Term	3 years 6 months 4 days	3 years 7 months 17 days
Vested and expected to vest, Average Remaining Contractual Term	3 years 5 months 23 days
Options exercisable, Average Remaining Contractual Term	2 years 11 months 12 days
Options outstanding, Aggregate Intrinsic Value	$ 12,436	$ 12,595
Vested and expected to vest, Aggregate Intrinsic Value	12,347
Options exercisable, Aggregate Intrinsic Value	$ 10,420