Fair Value Measurements (Assets And Liabilities Measured On Recurring Basis) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Assets:
Restricted cash, primarily money market funds	$ 13,635		$ 13,635		$ 12,793
Liabilities:
Gain included in interest and other income/expense	5,100	$ 1,700	(900)	$ 5,200	9,400
Equity securities, unrealized gain (loss)	4,400	$ 900	(1,900)	$ 3,900	6,700
Recurring [Member]
Assets:
Assets, fair value disclosure	48,637		48,637		76,624
Liabilities:
Deferred compensation plan obligations	37,314		37,314		38,378
Total	37,314		37,314		38,378
Recurring [Member] | Money Market Funds [Member]
Assets:
Cash equivalents	153		153		28,330
Restricted cash, primarily money market funds	11,170		11,170		9,916
Recurring [Member] | Grantor Trusts [Member]
Assets:
Investments	37,314		37,314		38,378
Recurring [Member] | Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member]
Assets:
Assets, fair value disclosure	48,637		48,637		76,624
Liabilities:
Deferred compensation plan obligations	37,314		37,314		38,378
Total	37,314		37,314		38,378
Recurring [Member] | Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member] | Money Market Funds [Member]
Assets:
Cash equivalents	153		153		28,330
Restricted cash, primarily money market funds	11,170		11,170		9,916
Recurring [Member] | Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member] | Grantor Trusts [Member]
Assets:
Investments	37,314		37,314		38,378
Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Assets, fair value disclosure	0		0		0
Liabilities:
Total	0		0		0
Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets:
Assets, fair value disclosure	0		0		0
Liabilities:
Total	$ 0		$ 0		$ 0