Fair Value Measurements (Assets And Liabilities Measured On Recurring Basis) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Assets:
Restricted cash, primarily money market funds	$ 60,925		$ 60,925		$ 8,150
Liabilities:
Gain included in interest and other income/expense	1,100	$ 1,200	6,300	$ 3,900
Equity securities, unrealized gain (loss)	200	$ 800	4,100	$ 400
Recurring [Member]
Assets:
Assets, fair value disclosure	154,972		154,972		97,733
Liabilities:
Deferred compensation plan obligations	35,740		35,740		30,996
Total	35,740		35,740		30,996
Recurring [Member] | Money Market Funds, Bank TIme Deposits, and Commercial Paper [Member]
Assets:
Cash equivalents	108,895		108,895
Recurring [Member] | Money Market Funds [Member]
Assets:
Cash equivalents					54,848
Restricted cash, primarily money market funds	10,337		10,337		5,254
Recurring [Member] | Grantor Trusts [Member]
Assets:
Investments	35,740		35,740		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	154,972		154,972		97,733
Liabilities:
Deferred compensation plan obligations	35,740		35,740		30,996
Total	35,740		35,740		30,996
Recurring [Member] | Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member] | Money Market Funds, Bank TIme Deposits, and Commercial Paper [Member]
Assets:
Cash equivalents	108,895		108,895
Recurring [Member] | Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member] | Money Market Funds [Member]
Assets:
Cash equivalents					54,848
Restricted cash, primarily money market funds	10,337		10,337		5,254
Recurring [Member] | Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member] | Grantor Trusts [Member]
Assets:
Investments	35,740		35,740		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