Fair Value Measurements (Financial Assets And Liabilities Measured At Fair Value) (Details) - USD ($) $ in Thousands	3 Months Ended			12 Months Ended
	Mar. 31, 2018		Mar. 31, 2017	Dec. 31, 2017
Deferred compensation plan investments (1)	$ 119,000	[1]		$ 120,300
Participant Withdrawals From Deferred Compensation Plan Investments	3,000		$ 4,200
Diversification of share awards within deferred compensation plan			$ 1,642	23,200
Interest Rate Derivative Assets, at Fair Value	7,700			2,200
Interest Rate Derivative Liabilities, at Fair Value	2,400			500
Level 1 [Member]
Deferred compensation plan investments (1)	119,000	[1]		120,300
Interest Rate Derivative Assets, at Fair Value	0			0
Interest Rate Derivative Liabilities, at Fair Value	0			0
Level 2 [Member]
Deferred compensation plan investments (1)	0	[1]		0
Level 3 [Member]
Deferred compensation plan investments (1)	0	[1]		0
Interest Rate Derivative Assets, at Fair Value	0			0
Interest Rate Derivative Liabilities, at Fair Value	0			0
Interest Rate Swap [Member]
Interest Rate Derivative Assets, at Fair Value	7,700			2,200
Interest Rate Derivative Liabilities, at Fair Value	2,400			500
Interest Rate Swap [Member] | Level 2 [Member]
Interest Rate Derivative Assets, at Fair Value	7,700			2,200
Interest Rate Derivative Liabilities, at Fair Value	$ 2,400			$ 500

[1] Approximately $3.0 million and $4.2 million of participant cash was withdrawn from our deferred compensation plan investments during the three months ended March 31, 2018 and the year ended December 31, 2017, respectively. Approximately $23.2 million of shares in the compensation plan were diversified into the deferred compensation plan investments during the year ended December 31, 2017.