Goodwill & Other Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Roll Forward]
Goodwill	$ 160,252	$ 143,189	$ 137,392
Accumulated impairment losses	(15,417)	(15,417)	(15,417)
Acquisitions	12,710
Foreign currency translation	4,353	(4,142)
Total	144,835	127,772	121,975
Learning Solutions [Member]
Goodwill [Roll Forward]
Goodwill	60,948	51,158	51,901
Accumulated impairment losses	(2,079)	(2,079)	(2,079)
Acquisitions	6,424
Foreign currency translation	3,366	(2,571)
Total	58,869	49,079	49,822
Professional and Technical Services [Member]
Goodwill [Roll Forward]
Goodwill	50,873	50,194	51,532
Accumulated impairment losses	(7,830)	(7,830)	(7,830)
Acquisitions	0
Foreign currency translation	679	(1,338)
Total	43,043	42,364	43,702
Sandy Training and Marketing [Member]
Goodwill [Roll Forward]
Goodwill	6,161	6,161	6,161
Accumulated impairment losses	(5,508)	(5,508)	(5,508)
Acquisitions	0
Foreign currency translation	0	0
Total	653	653	653
Performance Readiness Group [Member]
Goodwill [Roll Forward]
Goodwill	42,270	35,676	27,798
Accumulated impairment losses	0	0	0
Acquisitions	6,286
Foreign currency translation	308	(233)
Total	$ 42,270	$ 35,676	$ 27,798