Income Taxes - Reconciliation Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	May 31, 2020	May 31, 2019
Reconciliation of Unrecognized Tax Benefits [Roll Forward]
Balance at beginning of period	$ 48,715	$ 36,647
Additions for tax positions of the current year	3,976	3,641
Additions for tax positions of prior years	4,325	10,239
Settlements	(5,473)
Statute expirations	(6,873)	(1,812)
Balance at end of period	$ 44,670	$ 48,715