Income Taxes (Schedule Of Components Of Net Deferred Tax Assets And Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets
Accrued expenses	$ 13,843	$ 22,145
Accounts receivable reserves	2,624	2,715
Deferred revenue	10,618	13,400
Inventory basis differences	3,039	3,959
Property-based differences	1,324	1,382
Share-based compensation	9,035	13,021
Other	918	678
Net operating loss carryforwards	3,350	4,182
Tax credit carryforwards	8,096
Unrealized losses on foreign currency exchange contracts, interest rate swaps and investments	2,355	148
Total assets	55,202	61,630
Valuation allowance	(6,211)	(4,891)
Total assets, net of valuation allowance	48,991	56,739
Liabilities
Deferred instrument costs	(20,399)	(24,142)
Property-based differences	(31,859)	(43,159)
Intangible assst basis differences	(13,574)	(17,672)
Other	(656)	(771)
Unrealized gains on foreign currency exchange contracts, interest rate swaps and investments	(158)	(4,575)
Total liabilities	(66,646)	(90,319)
Net deferred tax assets (liabilities)	$ (17,655)	$ (33,580)