Investments - Narrative (Details) - USD ($)	3 Months Ended	9 Months Ended
Nov. 30, 2018	Feb. 28, 2019	Feb. 28, 2018	May 31, 2018
Investments, Debt and Equity Securities [Abstract]
Investments		$ 191,818,000		$ 175,581,000
Cash surrender value of insurance policies		170,200,000		154,000,000
Equity method investments		18,400,000		16,400,000
Cost method investments		3,200,000		$ 5,200,000
Losses due to impairment		0	$ 0
Proceeds from sale of a cost method investment	$ 73,300,000	$ 73,342,000	$ 0
Pre-tax gain on sale of cost method investment	$ 69,400,000

Carrying amount as of the balance sheet date of amounts which could be received based on the terms of the insurance contract upon surrendering life policies owned by the entity.

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This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized.

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Cost of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). Excludes equity method investment and investment in equity security without readily determinable fair value.

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Amount of gain (loss) included in earnings for investments classified as other.

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Sum of the carrying amounts as of the balance sheet date of all investments.

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Amount of cash inflow from the sale of investments classified as other.

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