Stockholders' Equity (Details 1) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Summary of stock options activity
Granted, Number of options	0	0
Stock Options [Member]
Summary of stock options activity
Options outstanding, beginning of period	6,321,076
Weighted average exercise price, Options outstanding, beginning of period	6.05
Granted, Number of options
Weighted average exercise price, Granted
Number of options, Exercised	(242,678)
Weighted average exercise price, Exercised	1.25
Number of options, Expired / forfeited	(24,027)
Weighted average exercise price, Expired / forfeited	4.81
Options outstanding, end of period	6,054,371
Weighted average exercise price, Options outstanding, end of period	6.25
Options exercisable, end of period	5,218,671
Weighted average exercise price, Options exercisable, end of period	6.49
Options expected to vest, end of period	642,255
Weighted average exercise price, Options expected to vest, end of period	4.58
Balance at March 31, 2013, Average Remaining Contractual Life (years)	4 years 10 months 17 days
Exercisable at March 31, 2013, Average Remaining Contractual Life (years)	4 years 6 months 11 days
Expected to vest after March 31, 2013, Average Remaining Contractual Life (years)	6 years 8 months 12 days
Aggregate intrinsic value, option outstanding	12,835,996
Aggregate intrinsic value, options exercisable	10,133,307
Expected to vest after March 31, 2013	2,162,786