Income Taxes - Reconciliation to federal statutory rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income tax provision reconciliation to federal statutory rate
Federal income taxes at statutory rate	$ 4,964	$ 9,267	$ 14,792
State income taxes, net of federal benefit	505	2,685	1,349
Goodwill impairment	1,883	0	428
Foreign taxes	2,276	2,150	(3,226)
Change in valuation allowance	3,919	9,540	2,913
Research and development credits	(626)	(273)	(448)
Foreign tax credits	(283)	(429)	(2,002)
Nondeductible meals and entertainment	724	782	1,222
US tax reform - revaluation of deferred taxes	0	102	(3,756)
US tax reform - transition tax, net of credits	0	(3,496)	7,550
Income tax planning	0	(1,792)	0
Benefit of international restructuring	0	0	(2,989)
Global intangible low-tax income, net of credits	892	454	0
Foreign-derived intangible income deduction	(315)	(323)	0
Tax rate changes	486	(392)	(212)
Other	(314)	267	(582)
Provision for income taxes	$ 14,111	$ 18,542	$ 15,039