Investments - Narrative (Details) - USD ($)	12 Months Ended
	May 31, 2018		May 31, 2017		May 31, 2016
Investments [Abstract]
Investments	$ 175,581,000	[1]	$ 164,788,000	[2]
Cash surrender value of life insurance policies	154,000,000		144,000,000
Equity method investments	16,400,000		15,800,000
Cost method investments	5,200,000		5,000,000
Losses due to impairment	$ 0		$ 0		$ 0

[1] Investments include inter company investment activity. Corp 2 and Subsidiary Guarantors hold $17.6 million and $158.0 million, respectively, of the $175.6 million consolidated net investments.

[2] Investments include inter company investment activity. Corp 2 and Subsidiary Guarantors hold $29.0 million and $135.8 million, respectively, of the $164.8 million consolidated net investments.