Share Based Compensation (Details 2) (Performance Share Units [Member], USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011
Performance Share Units [Member]
Performance share units
Outstanding at the beginning of year, nonvested	1,897
Grants in periods, number of shares	445
Vested in periods, number of shares	(1,250)
Forfeited RSU's, number of shares	(233)
Outstanding at the end of year, nonvested	859
Outstanding at the beginning of year, weighted average grant date fair value	$ 9.59
Grants in periods, weighted average grant date fair value	$ 26.25
Vested in periods, weighted average grant date fair value	$ (5.65)
Forfeited RSU's, weighted average grant date fair value	$ (13.23)
Outstanding at the end of year, weighted average grant date fair value	$ 22.98