Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets related to:
Accrued liabilities	$ 1,105		$ 1,226
Intangible assets	3,054		3,010
Net operating loss carryforward	15,970		6,912
Valuation allowance	(14,326)		(3,942)
Non-qualified stock options	672		762
Foreign tax credits	1,489		1,751
Valuation allowance on foreign tax credits	1,489		1,514
Goodwill	8,200		0
Other	2,684		215
Total assets	17,359		8,420
Liabilities related to:
Depreciation and amortization	(16,974)		(15,788)
Goodwill	0		(5,178)
Deferred revenue on maintenance contracts	(434)		(597)
Other	0		(100)
Total liabilities	(17,408)		(21,663)
Net non-current deferred tax liabilities	$ (49)	$ (13,167)	$ (13,243)