Share - Based Compensation (Details 1) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012
Restricted stock units payable in Stock [Member]
Restricted stock units
Outstanding at the beginning of year, nonvested	638
Grants in periods, number of shares	367
Vested in periods, number of shares	(218)
Forfeited RSU's, number of shares	(13)
Outstanding at the end of year, nonvested	774
Outstanding at the beginning of year, weighted average grant date fair value	$ 35.53
Grants in periods, weighted average grant date fair value	$ 27.54
Vested in periods, weighted average grant date fair value	$ (37.89)
Forfeited in period, weighted average grant date fair value	$ (33.19)
Outstanding at the end of year, weighted average grant date fair value	$ 31.12
Restricted stock units payable in cash [Member]
Restricted stock units
Outstanding at the beginning of year, nonvested	2,927
Grants in periods, number of shares	808
Vested in periods, number of shares	(801)
Forfeited RSU's, number of shares	(73)
Outstanding at the end of year, nonvested	2,861
Outstanding at the beginning of year, weighted average grant date fair value	$ 17.33
Grants in periods, weighted average grant date fair value	$ 27.74
Vested in periods, weighted average grant date fair value	$ (15.00)
Forfeited in period, weighted average grant date fair value	$ (19.24)
Outstanding at the end of year, weighted average grant date fair value	$ 20.88