Significant Accounting Policies (Schedule Of Allowance For Doubtful Accounts) (Details) - Allowance For Doubtful Accounts [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of year	$ 12,920	$ 14,139	$ 10,300
Additions charged to expense	1,051	1,552	3,766
Other			73
Other, deductions	(3,713)	(2,771)
Balance at end of year	$ 10,258	$ 12,920	$ 14,139