Fair Value Measurements (Assets And Liabilities Measured On Recurring Basis) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Assets:
Restricted cash, primarily money market funds	$ 13,349		$ 13,349		$ 8,150
Liabilities:
Gain included in interest and other income/expense	1,700	$ 1,200	5,200	$ 2,700
Equity securities, unrealized gain (loss)	900	$ (800)	3,900	$ (400)
Recurring [Member]
Assets:
Assets, fair value disclosure	153,229		153,229		97,733
Liabilities:
Deferred compensation plan obligations	35,434		35,434		30,996
Total	35,434		35,434		30,996
Recurring [Member] | Money Market Funds [Member]
Assets:
Cash equivalents	108,937		108,937		54,848
Restricted cash, primarily money market funds	8,858		8,858		5,254
Recurring [Member] | Grantor Trusts [Member]
Assets:
Investments	35,434		35,434		30,996
Recurring [Member] | Mutual Funds [Member]
Assets:
Investments					6,635
Recurring [Member] | Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member]
Assets:
Assets, fair value disclosure	153,229		153,229		97,733
Liabilities:
Deferred compensation plan obligations	35,434		35,434		30,996
Total	35,434		35,434		30,996
Recurring [Member] | Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member] | Money Market Funds [Member]
Assets:
Cash equivalents	108,937		108,937		54,848
Restricted cash, primarily money market funds	8,858		8,858		5,254
Recurring [Member] | Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member] | Grantor Trusts [Member]
Assets:
Investments	35,434		35,434		30,996
Recurring [Member] | Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member] | Mutual Funds [Member]
Assets:
Investments					6,635
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