Stock-based Compensation (Stock Option Activity) (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013		Jun. 30, 2013
Stock-based Compensation [Abstract]
Outstanding at December 31, 2012, shares			4,685,434
Options granted, shares			236,411
Options exercised, shares			(163,615)
Options forfeited, shares			(64,949)
Options cancelled or expired, shares			(87,568)
Outstanding at June 30, 2013, shares	4,605,713		4,605,713
Vested or expected to vest at June 30, 2013, shares	4,569,281	[1]	4,569,281	[1]
Exercisable at June 30, 2013, shares	3,694,946		3,694,946
Outstanding at December 31, 2012, exercise price			$ 3.82
Options granted, exercise price			$ 3.50
Options exercised, exercise price			$ 1.57
Options forfeited, exercise price			$ 4.35
Options cancelled or expired, exercise price			$ 6.61
Outstanding at June 30, 2013, exercise price	$ 3.83		$ 3.83
Vested or expected to vest at June 30, 2013, exercise price	$ 3.82	[1]	$ 3.82	[1]
Exercisable at June 30, 2013, exercise price	$ 3.52		$ 3.52
Outstanding at June 30, 2013, contractual life			4 years 10 months 6 days
Vested or expected to vest at June 30, 2013, contractual life			4 years 10 months 6 days	[1]
Exercisable at June 30, 2013, contractual life			5 years 11 days
Outstanding at June 30, 2013, intrinsic value	$ 3,901,599		$ 3,901,599
Vested or expected to vest at June 30, 2013, intrinsic value	3,896,971	[1]	3,896,971	[1]
Exercisable at June 30, 2013, intrinsic value	3,785,907		3,785,907
Aggregate intrinsic value of options exercised	$ 325,000		$ 344,000

[1] The expected to vest options are the result of applying the pre-vesting forfeiture rate assumptions to total unvested options