Fair Value Measurements (Schedule Of Assets And Liabilities Carried At Fair Value Measured On A Recurring Basis) (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash and cash equivalents		$ 467,430	$ 464,617
Restricted cash		1,958	2,043
Deferred compensation plan assets		22,054	12,153
Total		491,442	478,813
Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash and cash equivalents	[1]	467,430	464,617
Restricted cash	[2]	1,958	2,043
Deferred compensation plan assets	[3]	22,054	12,153
Total		491,442	478,813
Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash and cash equivalents	[1]	0	0
Restricted cash	[2]	0	0
Deferred compensation plan assets	[3]	0	0
Total		0	0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash and cash equivalents	[1]	0	0
Restricted cash	[2]	0	0
Deferred compensation plan assets	[3]	0	0
Total		0	0
Money Market Funds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash and cash equivalents		$ 194,200	$ 154,600

[1] Cash and cash equivalents consist primarily of money market funds with original maturity dates of three months or less, which are Level 1 assets. At December 31, 2017 and 2016, we had $194.2 million and $154.6 million, respectively, in money market funds.

[2] Restricted cash is classified as “Prepaid expenses and other” in the Consolidated Balance Sheets.

[3] Deferred compensation plan assets are classified as “Other assets” in the Consolidated Balance Sheets.