Income Taxes (Schedule Of Deferred Tax Assets And Deferred Tax Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Abstract]
Accounts receivable	$ 68	$ 307
Accrued expenses and other current liabilities	886	423
Unearned revenue	198	856
Stock-based compensation	744	2,280
Other	89	616
Net operating loss carry forwards	34,758	27,225
Gross deferred tax assets	36,743	31,707
Net deferred tax assets	36,743	31,707
Intangible assets	1,734	2,946
Depreciation and amortization	65,609	73,305
Foreign deferred tax liabilities	943	760
Deferred subpart F income	4,310	6,500
Gross deferred tax liabilities	72,596	83,511
Net deferred tax liability	$ 35,853	$ 51,804