Stock-based compensation Share-based Compensation, Nonvested Share Activity (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number	2,565	1,564
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value	$ 18.23	$ 18.08
Share-based Compensation Arrangement by Share-based Payment Award, Stock Options, Grants in Period	1,761
Share-based Compensation Arrangement by Share-based Payment Award, Stock Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 19.12
Share-based Compensation Arrangement by Share-based Payment Award, Stock Options, Vested in Period	(720)
Share-based Compensation Arrangement by Share-based Payment Award, Stock Options, Vested in Period, Weighted Average Grant Date Fair Value	$ 20.67
Share-based Compensation Arrangement by Share-based Payment Award, Stock Options, Forfeited in Period	(40)
Share-based Compensation Arrangement by Share-based Payment Award, Stock Options, Forfeited in Period, Weighted Average Grant Date Fair Value	$ 18.84