Share-Based Compensation and Equity - Share-based Compensation Expense (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Pre-tax compensation expense	$ 14,296	$ 12,541	$ 11,910
Tax benefit	(4,912)	(4,640)	(4,407)
Compensation expense, net of tax	9,384	7,901	7,503
Stock Options [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Pre-tax compensation expense	3,486	3,540	3,127
Tax benefit	(1,238)	(1,310)	(1,157)
Compensation expense, net of tax	2,248	2,230	1,970
Restricted Stock Units [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Pre-tax compensation expense	5,734	4,355	3,775
Tax benefit	(1,845)	(1,611)	(1,397)
Compensation expense, net of tax	3,889	2,744	2,378
Performance Shares [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Pre-tax compensation expense	4,076	3,820	4,192
Tax benefit	(1,459)	(1,413)	(1,551)
Compensation expense, net of tax	2,617	2,407	2,641
Director Deferred Shares [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Pre-tax compensation expense	1,000	826	816
Tax benefit	(370)	(306)	(302)
Compensation expense, net of tax	$ 630	$ 520	$ 514