Debt (Components Of Debt) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2012 Variable Rate 2.200% and 2.276% [Member]	Dec. 31, 2011 Variable Rate 2.200% and 2.276% [Member]	Sep. 30, 2012 7.5% Senior Notes due 2018 [Member]	Dec. 31, 2011 7.5% Senior Notes due 2018 [Member]	Sep. 30, 2012 7.35% Senior Notes due 2017 [Member]	Dec. 31, 2011 7.35% Senior Notes due 2017 [Member]	Sep. 30, 2012 7.125% Senior Notes due 2017 [Member]	Dec. 31, 2011 7.125% Senior Notes due 2017 [Member]	Sep. 30, 2012 7.15% Senior Notes due 2018 [Member]	Dec. 31, 2011 7.15% Senior Notes due 2018 [Member]	Sep. 30, 2012 4.10% Senior Notes Due 2022 [Member]	Mar. 31, 2012 4.10% Senior Notes Due 2022 [Member]
Debt Instrument [Line Items]
Total short-term debt	$ 1,200	$ 1,200									$ 1,200	$ 1,200
Variable rate (2.200% and 2.276% at September 30, 2012 and December 31, 2011, respectively) unsecured revolving credit facility, expires February 2016			26,500	671,500
Unamortized discount	(1,158)
Senior Notes					600,000	600,000	15,000	15,000	25,000	25,000	30,000	30,600	1,000,000	1,000,000
Long-term debt	1,695,342	1,342,100
Total debt	$ 1,696,542	$ 1,343,300
Debt instrument, interest rate, stated percentage			2.20%	2.276%	7.50%		7.35%		7.125%		7.15%		4.10%	4.10%