Fair Value Measurements (Assets And Liabilities Measured On Recurring Basis) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Assets:
Restricted cash, primarily commercial paper and mutual funds (1)	$ 19,851	$ 19,851	$ 6,291
Liabilities:
Gain included in interest and other income/expense	1,200	2,700
Unrealized gain (loss) included in interest and other income/expense	(800)	(400)
Recurring [Member]
Assets:
Total	52,435	52,435	40,738
Liabilities:
Deferred compensation plan obligations	32,656	32,656	31,497
Total	32,656	32,656	31,497
Recurring [Member] | Money Market Funds [Member]
Assets:
Cash equivalents, primarily money market funds (1)	6,986	6,986
Recurring [Member] | Commercial Paper And Mutual Fund [Member]
Assets:
Restricted cash, primarily commercial paper and mutual funds (1)	5,447	5,447
Recurring [Member] | Grantor Trusts [Member]
Assets:
Investments	32,656	32,656	31,497
Recurring [Member] | Mutual Funds [Member]
Assets:
Investments	7,346	7,346	7,206
Recurring [Member] | Interest Rate Contracts [Member]
Assets:
Derivative assets			2,035
Recurring [Member] | Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member]
Assets:
Total	52,435	52,435	38,703
Liabilities:
Deferred compensation plan obligations	32,656	32,656	31,497
Total	32,656	32,656	31,497
Recurring [Member] | Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member] | Money Market Funds [Member]
Assets:
Cash equivalents, primarily money market funds (1)	6,986	6,986
Recurring [Member] | Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member] | Commercial Paper And Mutual Fund [Member]
Assets:
Restricted cash, primarily commercial paper and mutual funds (1)	5,447	5,447
Recurring [Member] | Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member] | Grantor Trusts [Member]
Assets:
Investments	32,656	32,656	31,497
Recurring [Member] | Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member] | Mutual Funds [Member]
Assets:
Investments	7,346	7,346	7,206
Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Total	0	0	2,035
Liabilities:
Total	0	0	0
Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Interest Rate Contracts [Member]
Assets:
Derivative assets			2,035
Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets:
Total	0	0	0
Liabilities:
Total	$ 0	$ 0	$ 0