Stock-based compensation Share-based Compensation, Nonvested Share Activity (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number	3,678	3,690
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value	$ 17.72	$ 17.69
Share-based Compensation Arrangement by Share-based Payment Award, Stock Options, Grants in Period	12
Share-based Compensation Arrangement by Share-based Payment Award, Stock Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 26.26
Share-based Compensation Arrangement by Share-based Payment Award, Stock Options, Vested in Period	(6)
Share-based Compensation Arrangement by Share-based Payment Award, Stock Options, Vested in Period, Weighted Average Grant Date Fair Value	$ 17.95
Share-based Compensation Arrangement by Share-based Payment Award, Stock Options, Forfeited in Period	(18)
Share-based Compensation Arrangement by Share-based Payment Award, Stock Options, Forfeited in Period, Weighted Average Grant Date Fair Value	$ 17.65