Fair Value Measurements (Assets And Liabilities Measured On Recurring Basis) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Assets:
Restricted cash, primarily money market funds	$ 13,891		$ 13,891		$ 12,793
Liabilities:
Gain included in interest and other income/expense	2,100	$ 1,100	1,200	$ 6,300	9,400
Equity securities, unrealized gain (loss)	1,700	$ 200	(200)	$ 4,100	6,700
Recurring [Member]
Assets:
Assets, fair value disclosure	51,052		51,052		76,624
Liabilities:
Deferred compensation plan obligations	39,476		39,476		38,378
Total	39,476		39,476		38,378
Recurring [Member] | Money Market Funds [Member]
Assets:
Cash equivalents	155		155		28,330
Restricted cash, primarily money market funds	11,421		11,421		9,916
Recurring [Member] | Grantor Trusts [Member]
Assets:
Investments	39,476		39,476		38,378
Recurring [Member] | Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member]
Assets:
Assets, fair value disclosure	51,052		51,052		76,624
Liabilities:
Deferred compensation plan obligations	39,476		39,476		38,378
Total	39,476		39,476		38,378
Recurring [Member] | Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member] | Money Market Funds [Member]
Assets:
Cash equivalents	155		155		28,330
Restricted cash, primarily money market funds	11,421		11,421		9,916
Recurring [Member] | Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member] | Grantor Trusts [Member]
Assets:
Investments	39,476		39,476		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