Goodwill & Other Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Goodwill	$ 191,541	$ 160,252	$ 143,189
Accumulated impairment losses	(15,417)	(15,417)	(15,417)
Acquisitions	35,646	12,710
Foreign currency translation	(4,357)	4,353
Total	176,124	144,835	127,772
Professional and Technical Services [Member]
Goodwill [Roll Forward]
Goodwill	58,573	45,438	38,844
Accumulated impairment losses	(6,367)	(6,367)	(6,367)
Acquisitions	14,033	6,286
Foreign currency translation	(898)	308
Total	52,206	39,071	32,477
Sandy Training and Marketing [Member]
Goodwill [Roll Forward]
Goodwill	132,968	114,814	104,345
Accumulated impairment losses	(9,050)	(9,050)	(9,050)
Acquisitions	21,613	6,424
Foreign currency translation	(3,459)	4,045
Total	$ 123,918	$ 105,764	$ 95,295