Debt (Components Of Debt) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 7.5% Senior Notes due 2018 [Member]	Dec. 31, 2011 7.5% Senior Notes due 2018 [Member]	Dec. 31, 2012 7.35% Senior Notes due 2017 [Member]	Dec. 31, 2011 7.35% Senior Notes due 2017 [Member]	Dec. 31, 2012 7.125% Senior Notes due 2017 [Member]	Dec. 31, 2011 7.125% Senior Notes due 2017 [Member]	Dec. 31, 2012 7.15% Senior Notes due 2018 [Member]	Dec. 31, 2011 7.15% Senior Notes due 2018 [Member]	Dec. 31, 2012 4.10% Senior Notes Due 2022 [Member]	May 31, 2012 4.10% Senior Notes Due 2022 [Member]	Dec. 31, 2012 Parent [Member]	Dec. 31, 2011 Parent [Member]
Debt Instrument [Line Items]
7.15 % Senior Notes due 2018	$ 1,200	$ 1,200
Total short-term debt	1,200	1,200
Variable rate (2.200% and 2.276% at December 31, 2012 and December 31, 2011, respectively) unsecured revolving credit facility, expires February 2016		671,500
Unamortized discount	(1,127)
Senior Notes			600,000	600,000	15,000	15,000	25,000	25,000	29,400	30,600	1,000,000	1,000,000
Debt instrument, interest rate, stated percentage			7.50%		7.35%		7.125%				4.10%	4.10%
Long-term debt maturing 2013	1,200
Long-term debt maturing 2014	1,200
Long-term debt maturing 2015	1,200
Long-term debt maturing 2016	41,200
Long-term debt maturing thereafter	1,624,600
Total long-term debt	1,668,273	1,342,100											1,668,273	1,342,100
Total debt	1,669,473	1,343,300
Total future maturities of long term debt	$ 1,669,400