Share-Based Compensation (Details 2) (USD $)	12 Months Ended						3 Months Ended	12 Months Ended
	Dec. 31, 2012 2005 Plan Stock options	Dec. 31, 2011 2005 Plan Stock options	Dec. 31, 2010 2005 Plan Stock options	Dec. 31, 2012 2005 Plan Restricted common stock	Dec. 31, 2011 2005 Plan Restricted common stock	Dec. 31, 2010 2005 Plan Restricted common stock	Mar. 31, 2013 2005 Plan Restricted common stock Subsequent event	Dec. 31, 2012 Director compensation plan Restricted common stock Board of directors item	Dec. 31, 2011 Director compensation plan Restricted common stock Board of directors item	Dec. 31, 2010 Director compensation plan Restricted common stock Board of directors item
Number of Shares Underlying Options
Outstanding at the beginning of the period (in shares)	1,715,358	1,741,543
Granted (in shares)	34,500	1,453,240
Exercised (in shares)	(15,463)	(25,036)
Cancelled/forfeited (in shares)	(58,976)	(1,454,389)
Outstanding at the end of the period (in shares)	1,675,419	1,715,358	1,741,543
Exercisable at the end of the period (in shares)	522,870
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 4.35	$ 8.84
Granted (in dollars per share)	$ 3.23	$ 4.79
Exercised (in dollars per share)	$ 2.43	$ 2.42
Cancelled/forfeited (in dollars per share)	$ 3.89	$ 10.20
Outstanding at the end of the period (in dollars per share)	$ 4.36	$ 4.35	$ 8.84
Exercisable at the end of the period (in dollars per share)	$ 4.01
Intrinsic Value
Outstanding at the beginning of the period	$ 114,189	$ 700,174
Exercised	30,745	17,251
Cancelled/forfeited	65,302	42,039
Outstanding at the end of the period	69,712	114,189	700,174
Exercisable at the end of the period	48,425
Additional disclosures
Compensation expense	500,000	600,000	300,000	2,000,000	1,400,000	1,500,000
Estimated expenses that will be expensed over the remaining vesting period				3,600,000
Shares issued				959,000	446,725	402,859		54,879	39,267	31,646
Shares forfeited				33,500	43,020	22,000
Award vesting period				4 years	4 years	4 years
Number of members of board of directors to whom shares are issued as compensation								3	3	2
Fair value on the grant date								$ 3,300,000	$ 1,800,000	$ 1,200,000
Shares
Non-vested at the beginning of the period (in shares)				1,207,313	1,268,037
Granted (in shares)				1,013,879	485,992		632,000
Vested (in shares)				(393,127)	(354,051)
Cancelled/forfeited (in shares)				(43,601)	(192,665)
Non-vested at the end of the period (in shares)				1,784,464	1,207,313	1,268,037
Weighted-Average Grant Date Fair Value
Non-vested at the beginning of the period (in dollars per share)				$ 3.36	$ 3.28
Granted (in dollars per share)				$ 3.26	$ 3.78
Vested (in dollars per share)				$ 3.23	$ 3.48
Forfeited (in dollars per share)				$ 3.23	$ 3.70
Non-vested at the end of the period (in dollars per share)				$ 3.33	$ 3.36	$ 3.28
Granted (in shares)				1,013,879	485,992		632,000
Shares of common stock available to be awarded	1,100,000						515,380