Debt (Schedule Of Credit Facilities) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Line of Credit Facility [Line Items]
Balance outstanding	$ 149,500	$ 189,000
Maximum balance outstanding during the year	244,500	270,000
Weighted average balance	$ 100,506	$ 151,036
Year-to-date weighted average interest rate (excluding facility fee)	0.90%	0.80%
Unsecured Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Balance outstanding	$ 140,000	$ 189,000
Available balance	$ 355,190	$ 306,777
Variable interest rate	1.30%	0.80%
Letter of Credit [Member]
Line of Credit Facility [Line Items]
Letter of credit outstanding under facility	$ 4,810	$ 4,223
Unsecured Facility [Member]
Line of Credit Facility [Line Items]
Balance outstanding	$ 9,500	$ 0
Variable interest rate	1.70%	0.00%