Assets and Liabilities Measured at Fair Value on Recurring Basis and Categorized using Fair Value Hierarchy (Detail) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Feb. 29, 2020	May 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale debt securities	$ 25,490	$ 25,009
Total trading and other equity securities	102,226	99,821
Assets (liabilities) at fair value	112,068	103,279
U.S. Treasury and other government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale debt securities	25,045	24,547
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale debt securities	445	462
Stocks | Domestic
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total trading and other equity securities	2,789
Mutual funds | Foreign
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total trading and other equity securities	33,349	32,082
Mutual funds | Domestic
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total trading and other equity securities	66,088	67,739
Contingent consideration liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration	(15,648)	(21,551)
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total trading and other equity securities	2,789
Assets (liabilities) at fair value	2,789
Quoted Prices in Active Markets for Identical Assets (Level 1) | Stocks | Domestic
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total trading and other equity securities	2,789
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale debt securities	25,490	25,009
Total trading and other equity securities	99,437	99,821
Assets (liabilities) at fair value	124,927	124,830
Significant Other Observable Inputs (Level 2) | U.S. Treasury and other government
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale debt securities	25,045	24,547
Significant Other Observable Inputs (Level 2) | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale debt securities	445	462
Significant Other Observable Inputs (Level 2) | Mutual funds | Foreign
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total trading and other equity securities	33,349	32,082
Significant Other Observable Inputs (Level 2) | Mutual funds | Domestic
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total trading and other equity securities	66,088	67,739
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets (liabilities) at fair value	(15,648)	(21,551)
Significant Unobservable Inputs (Level 3) | Contingent consideration liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration	$ (15,648)	$ (21,551)