Debt (Schedule Of Debt Outstanding) (Details) (USD $)	0 Months Ended			3 Months Ended		3 Months Ended		3 Months Ended		3 Months Ended
	Jan. 06, 2012	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2012 Revolving Credit Facility [Member]	Dec. 31, 2011 Revolving Credit Facility [Member]	Mar. 31, 2012 Senior Notes 6.25% Due 2013 [Member]	Dec. 31, 2011 Senior Notes 6.25% Due 2013 [Member]	Mar. 31, 2012 Senior Notes 6.75% Due 2014 [Member]	Dec. 31, 2011 Senior Notes 6.75% Due 2014 [Member]	Mar. 31, 2012 Senior Notes 7.75% Due 2017 [Member]	Dec. 31, 2011 Senior Notes 7.75% Due 2017 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 1,180,386,000	$ 1,245,014,000	$ 535,000,000	$ 265,000,000	$ 40,000,000	$ 375,000,000	$ 150,000,000	$ 150,000,000	$ 455,386,000	$ 455,014,000
Revolving Credit Facility maturity date	December 2016
Note maturity date						Mar. 15, 2013		Jan. 31, 2014		Jun. 01, 2017
Weighted average rate				1.70%	1.00%
Interest rate stated percentage of Senior Notes						6.25%		6.75%		7.75%
Senior Notes interest payable dates				interest payable periodically at variable interest rates.		interest payable semi-annually in March and September at 6.25%.		interest payable semi-annually in January and July at 6.75%.		interest payable semi-annually in June and December at 7.75%.
Notes issued with a discount										13,400,000
Notes, unamortized										$ 9,600,000	$ 10,000,000