Stock Compensation (Details 2) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Stock Option Plan
Payments for employees' tax obligations			$ 426,000	$ 53,000
Cash received under all share-based arrangements			0
Restricted stock units
Stock Option Plan
Compensation expense	700,000	500,000	1,900,000	1,300,000
Fair value of restricted stock units vested			1,300,000	1,000,000
Shares withheld to cover withholding tax of unit holders			20,692	3,160
Payments for employees' tax obligations			400,000
Restricted stock units | Maximum
Stock Option Plan
Payments for employees' tax obligations				$ 100,000