Stockholders' Equity, Stock Option (Details) (Stock Options [Member], USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Stock Options [Member]
Stock option activity [Roll Forward]
Outstanding options, beginning balance (in shares)	5,382,391
Granted (in shares)	0
Exercised (in shares)	(25,454)
Forfeited (in shares)	(218,405)
Outstanding options, ending balance (in shares)	5,138,532	5,382,391
Options vested and expected to vest (in shares)	5,069,321
Exercisable options (in shares)	4,093,028
Options Outstanding, Weighted Average Exercise Price [Roll Forward]
Options outstanding, weighted average exercise price, beginning balance (in dollars per share)	$ 3.55
Granted, weighted average exercise price (in dollars per share)	$ 0
Exercised, weighted average exercise price (in dollars per share)	$ 2.34
Forfeited, weighted average exercise price (in dollars per share)	$ 4.21
Options outstanding, weighted average exercise price, ending balance (in dollars per share)	$ 3.53	$ 3.55
Vested and expected to vest, weighted average exercise price (in dollars per share)	$ 3.51
Exercisable, weighted average exercise price (in dollars per share)	$ 3.32
Additional Disclosures [Abstract]
Options outstanding, average remaining contractual term	2 years 7 months 10 days	3 years 7 months 28 days
Vested and expected to vest, average remaining contractual term	2 years 6 months 14 days
Options exercisable, average remaining contractual term	1 year 7 months 13 days
Options outstanding, aggregate intrinsic value	$ 455	$ 4,039
Vested and expected to vest, aggregate intrinsic value	454
Options exercisable, aggregate intrinsic value	$ 418