Debt (Summary Of Debt) (Details) (USD $)					3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended							3 Months Ended
	Mar. 31, 2012		Dec. 31, 2011		Mar. 31, 2012 Revolving Credit Facilities [Member]	Dec. 31, 2011 Revolving Credit Facilities [Member]	Mar. 31, 2012 2006 Senior Unsecured Notes [Member]	Dec. 31, 2011 2006 Senior Unsecured Notes [Member]	Mar. 31, 2012 2011 Senior Unsecured Notes [Member]	Dec. 31, 2011 2011 Senior Unsecured Notes [Member]	Mar. 31, 2012 2012 Senior Unsecured Notes [Member]	Feb. 17, 2012 2012 Senior Unsecured Notes [Member]	Mar. 31, 2012 Exchangeable Senior Notes [Member]	Dec. 31, 2011 Exchangeable Senior Notes [Member]	Mar. 31, 2012 Term Loans [Member]	Dec. 31, 2011 Term Loans [Member]
Debt Instrument [Line Items]
Principal amount						$ 89,600,000	$ 125,000,000	$ 125,000,000	$ 450,000,000	$ 450,000,000	$ 200,000,000		$ 11,000,000	$ 11,000,000
Unamortized discount													(147,000)	(180,000)
Debt instrument, net													10,853,000	10,820,000	114,372,000	14,429,000
Debt, net	$ 900,225,000	[1]	$ 689,849,000	[1]
Unsecured senior notes, interest rate									6.875%	6.875%	6.375%	6.375%		9.25%	9.25%	6.20%
Interest Rate					Variable	Variable	Various	Various							Various

[1] Level II: Fair value based on quoted prices for similar or identical instruments in active or inactive markets, respectively, or calculated utilizing model-derived valuations in which significant inputs or value drivers are observable in active markets.