Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current
Accrued liabilities	$ 0	$ 2,322
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Accrued Liabilities	1,226
Intangible assets	0	0
Non-qualified stock options	0	112
Other	0	45
Total assets	0	2,479
Long- term (a)
Intangible assets	3,010	4,517
Net operating loss carryforward	6,912	7,455
Valuation allowance	(3,942)	(3,321)
Non-qualified stock options	762	1,367
Foreign tax credits	1,751	2,035
Deferred Tax Assets, Tax Credit Carryforwards	(1,514)
AMT credits	0	780
Other	215	16
Total assets	8,420	12,849
Current
Deferred revenue on maintenance contracts	0	(429)
Other	0	(37)
Total liabilities	0	(466)
Net current deferred tax assets	0	2,013
Long-term
Depreciation and amortization	(15,788)	(25,326)
Goodwill	(5,178)	(6,502)
Deferred revenue on maintenance contracts	(597)	0
Other	(100)	(21)
Total liabilities	(21,663)	(31,849)
Net non-current deferred tax liabilities	$ (13,243)	$ (19,000)