Goodwill - Changes in Carrying Amount of Goodwill (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Goodwill [Line Items]
Gross goodwill, beginning of period	$ 482,707	$ 465,375
Goodwill acquired	9,125	43,584
Purchase accounting adjustments	(1,415)	(2,479)
Impact of foreign currency	(10,610)	(23,773)
Gross goodwill, end of period	479,807	482,707
Accumulated impairment loss, beginning of period	(41,500)	(22,600)
Impairment loss		(18,900)
Accumulated impairment loss, end of period	(41,500)	(41,500)
Net goodwill, end of period	438,307	441,207
CEB Segment [Member]
Goodwill [Line Items]
Gross goodwill, beginning of period	134,723	93,719
Goodwill acquired	9,125	43,584
Purchase accounting adjustments	(1,415)	(2,479)
Impact of foreign currency	(681)	(101)
Gross goodwill, end of period	141,752	134,723
Accumulated impairment loss, beginning of period	(41,500)	(22,600)
Impairment loss		(18,900)
Accumulated impairment loss, end of period	(41,500)	(41,500)
Net goodwill, end of period	100,252	93,223
SHL Talent Measurement Segment [Member]
Goodwill [Line Items]
Gross goodwill, beginning of period	347,984	371,656
Impact of foreign currency	(9,929)	(23,672)
Gross goodwill, end of period	338,055	347,984
Net goodwill, end of period	$ 338,055	$ 347,984