Debt (Schedule Of Credit Facilities) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Line of Credit Facility [Line Items]
Maximum balance outstanding during the period	$ 165,900	$ 265,500
Weighted average balance	121,227	61,642
Year-to-date weighted average interest rate (excluding facility fee)	0.80%	1.00%
Unsecured Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Balance outstanding	158,000	0
Available balance	338,946	497,821
Letters of credit outstanding under facility	3,054	2,179
Variable interest rate (excluding facility fee)	0.80%	0.00%
Unsecured And Uncommitted Overnight Facility [Member]
Line of Credit Facility [Line Items]
Balance outstanding	$ 1,900	$ 0
Variable interest rate (excluding facility fee)	1.50%	0.00%