Business Segments - EBITDA and Adjusted EBITDA (Details) - USD ($) $ in Thousands	3 Months Ended									6 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Jun. 30, 2017	Jun. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting [Abstract]
Adjusted EBITDA														$ 57,883	$ 58,612	$ 50,679
Depreciation and amortization		$ (3,317)	$ (3,182)	$ (2,904)		$ (5,066)	$ (4,720)	$ (4,596)		$ (6,086)	$ (9,316)	$ (9,403)	$ (14,382)	(13,390)	(17,916)	(17,472)
Stock-based compensation				(1,419)				(1,241)		(2,921)	(2,358)	(5,296)	(4,097)	(6,820)	(5,572)	(5,873)
Change in fair value of contingent consideration liability		(167)	1,884	(1,040)		788	7,276	1,911		844	9,187	677	9,975	677	10,417	(270)
Goodwill impairment charge									$ (37,500)					0	0	(37,539)
Intangible asset impairment charges	$ (100)				$ (100)				$ (202)					0	(70)	(202)
Restructuring and other charges														0
Restructuring charges		0	0	0		465	623	3,344		0	3,967	0	4,433	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		741	2,190	1,193		1,279	670	1,224		3,383	1,894	4,124	3,173	6,420	4,239	7,678
Income (loss) before income taxes		10,844	7,736	8,032		6,517	1,069	(1,026)		15,768	42	26,612	6,559	27,718	14,783	(20,891)
Interest income		31	12	34		26	24	14		46	38	77	63	97	86	69
Interest expense		$ 1,198	$ 1,038	$ 1,003		$ 1,190	$ 985	$ 1,077		$ 2,041	$ 2,062	$ 3,239	$ 3,252	$ 4,729	$ 4,171	$ 4,612