Segment Reporting and Related Disclosures Depreciation (Details) - USD ($) $ in Thousands	12 Months Ended
	May 31, 2016	May 31, 2015	May 31, 2014
Segment Reporting Information [Line Items]
Depreciation expense	$ 55,931	$ 56,445	$ 57,034
Operating Segments [Member] | T&M equipment
Segment Reporting Information [Line Items]
Depreciation expense	51,669	52,278	52,652
Operating Segments [Member] | DP equipment
Segment Reporting Information [Line Items]
Depreciation expense	$ 4,262	$ 4,167	$ 4,382