Business Segments - EBITDA and Adjusted EBITDA (Details) - USD ($) $ in Thousands	3 Months Ended			12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting [Abstract]
Adjusted EBITDA				$ 62,275	$ 59,153	$ 50,799
Depreciation and amortization				(13,390)	(17,916)	(17,472)
Stock-based compensation				(6,820)	(5,572)	(5,873)
Change in fair value of contingent consideration				(677)	(10,417)	270
Goodwill impairment charge			$ (37,500)	0	0	(37,539)
Intangible asset impairment charges	$ (100)	$ (100)	$ (200)	0	(70)	(202)
Restructuring and other charges				0	(5,615)	(1,053)
Business Development				(715)	0	0
Secured asset reserve				0	0	(2,023)
Professional fees related to ASC 606 implementation				(829)	0	0
Executive Succession Search Costs				(454)	0	0
Czech Koruna Appreciation Impact on Gross Profit				(860)	0	0
CEO search costs				(6,420)	(4,238)	(7,678)
Income (loss) before income taxes				32,110	15,325	(20,771)
Investment Income, Interest				97	86	69
Interest Expense				$ 4,729	$ 4,171	$ 4,612