Segment Data for our Three Operating Segment (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Nov. 30, 2013	Nov. 30, 2012	Nov. 30, 2013	Nov. 30, 2012
Segment Reporting Information [Line Items]
Revenues	$ 200,493	$ 200,648	$ 374,804	$ 362,140
Operating income	23,881	23,040	31,986	35,864
Capital expenditures	7,396	6,925	13,619	12,654
Depreciation and amortization	5,308	5,081	10,691	9,654
Operating Segments | IHT Segment
Segment Reporting Information [Line Items]
Revenues	109,427	108,935	205,260	191,145
Operating income	17,700	16,313	27,883	25,972
Capital expenditures	1,570	2,584	3,415	4,855
Depreciation and amortization	1,929	2,090	4,011	3,838
Operating Segments | MS Segment
Segment Reporting Information [Line Items]
Revenues	70,987	76,171	136,756	141,498
Operating income	7,380	10,459	14,181	17,703
Capital expenditures	1,751	1,825	3,191	4,612
Depreciation and amortization	1,812	1,685	3,590	3,394
Operating Segments | Quest Segment
Segment Reporting Information [Line Items]
Revenues	20,079	15,542	32,788	29,497
Operating income	5,512	2,985	4,816	6,006
Capital expenditures	719	876	2,675	1,401
Depreciation and amortization	1,365	1,175	2,690	2,155
Corporate and shared support services
Segment Reporting Information [Line Items]
Operating income	(6,711)	(6,717)	(14,894)	(13,817)
Capital expenditures	3,356	1,640	4,338	1,786
Depreciation and amortization	$ 202	$ 131	$ 400	$ 267