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, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Assets:
Restricted cash, primarily money market funds	$ 11,397		$ 11,397		$ 12,122
Liabilities:
Gain (loss) included in interest and other (Expense) Income	2,800	$ (5,100)	3,900	$ (900)	5,100
Equity securities, unrealized gain (loss)	2,500	$ (4,400)	3,600	$ (1,900)	3,700
Recurring [Member]
Assets:
Assets, fair value disclosure	56,451		56,451		53,711
Liabilities:
Deferred compensation plan obligations	47,310		47,310		43,412
Total	47,310		47,310		43,412
Recurring [Member] | Money Market Funds [Member]
Assets:
Cash equivalents	46		46		155
Restricted cash, primarily money market funds	9,095		9,095		10,144
Recurring [Member] | Grantor Trusts [Member]
Assets:
Investments, mutual funds held in a grantor trust	47,310		47,310		43,412
Recurring [Member] | Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member]
Assets:
Assets, fair value disclosure	56,451		56,451		53,711
Liabilities:
Deferred compensation plan obligations	47,310		47,310		43,412
Total	47,310		47,310		43,412
Recurring [Member] | Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member] | Money Market Funds [Member]
Assets:
Cash equivalents	46		46		155
Restricted cash, primarily money market funds	9,095		9,095		10,144
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	$ 47,310		$ 47,310		$ 43,412