Debt (Components Of Debt) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2012 Variable Rate 2.276% [Member]	Jun. 30, 2012 7.5% Senior Notes due 2018 [Member]	Dec. 31, 2011 7.5% Senior Notes due 2018 [Member]	Jun. 30, 2012 7.35% Senior Notes due 2017 [Member]	Dec. 31, 2011 7.35% Senior Notes due 2017 [Member]	Jun. 30, 2012 7.125% Senior Notes due 2017 [Member]	Dec. 31, 2011 7.125% Senior Notes due 2017 [Member]	Jun. 30, 2012 7.15% Senior Notes due 2018 [Member]	Dec. 31, 2011 7.15% Senior Notes due 2018 [Member]	Jun. 30, 2012 4.10% Senior Notes Due 2022 [Member]	Mar. 31, 2012 4.10% Senior Notes Due 2022 [Member]
Total short-term debt	$ 1,200	$ 1,200								$ 1,200	$ 1,200
Variable rate (2.200% and 2.276% at June 30, 2012 and December 31, 2011, respectively) unsecured revolving credit facility, expires February 2016		671,500
Unamortized discount	(1,189)
Total long-term debt	1,668,811	1,342,100		600,000	600,000	15,000	15,000	25,000	25,000	30,000	30,600	1,000,000	1,000,000
Total debt	$ 1,670,011	$ 1,343,300
Debt instrument, interest rate, stated percentage			2.276%	7.50%		7.35%		7.125%		7.15%		4.10%