Fair Value Measurements (Assets And Liabilities Measured On Recurring Basis) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Assets:
Restricted cash, primarily money market funds	$ 12,122	$ 12,793
Liabilities:
Gain included in interest and other income/expense	5,100	9,400
Equity securities, unrealized gain (loss)	3,700	6,700
Recurring [Member]
Assets:
Assets, fair value disclosure	53,711	76,624
Liabilities:
Deferred compensation plan obligations	43,412	38,378
Total	43,412	38,378
Recurring [Member] | Money Market Funds [Member]
Assets:
Cash equivalents	155	28,330
Restricted cash, primarily money market funds	10,144	9,916
Recurring [Member] | Grantor Trusts [Member]
Assets:
Investments, mutual funds held in a grantor trust	43,412	38,378
Recurring [Member] | Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member]
Assets:
Assets, fair value disclosure	53,711	76,624
Liabilities:
Deferred compensation plan obligations	43,412	38,378
Total	43,412	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	28,330
Restricted cash, primarily money market funds	10,144	9,916
Recurring [Member] | Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member] | Grantor Trusts [Member]
Assets:
Investments, mutual funds held in a grantor trust	$ 43,412	$ 38,378