INTANGIBLE ASSETS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Intangible assets
Gross Carrying Amount	$ 100,645	$ 73,399
Acquisitions		27,246
Accumulated Amortization	(74,675)	(65,161)
Currency impact	(286)	(371)
Net book value	25,684	35,113
Amortization expense	9,514	5,966	$ 5,323
Estimated future amortization expense
2018	4,942
2019	3,972
2020	3,397
2021	2,198
2022	1,757
Thereafter	9,418
Estimated future amortization expense	25,684
Customer relationships
Intangible assets
Gross Carrying Amount	73,723	54,450
Acquisitions		19,273
Accumulated Amortization	(55,844)	(47,303)
Currency impact	(105)	(151)
Net book value	17,774	26,269
Non-compete
Intangible assets
Gross Carrying Amount	5,952	5,670
Acquisitions		282
Accumulated Amortization	(5,754)	(5,686)
Currency impact	1	(1)
Net book value	199	265
Software
Intangible assets
Gross Carrying Amount	1,583	1,583
Accumulated Amortization	(1,520)	(1,501)
Currency impact	(63)	(78)
Net book value		4
Backlog
Intangible assets
Gross Carrying Amount	5,002	5,002
Accumulated Amortization	(4,981)	(4,974)
Currency impact	(21)	(28)
Databases
Intangible assets
Gross Carrying Amount	13,135	5,444
Acquisitions		7,691
Accumulated Amortization	(5,475)	(4,774)
Currency impact	(98)	(113)
Net book value	7,562	8,248
Trademarks And Trade Names
Intangible assets
Gross Carrying Amount	1,250	1,250
Accumulated Amortization	(1,101)	(923)
Net book value	$ 149	$ 327