Equity - Accumulated Other Comprehensive Income Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Nov. 30, 2019	Nov. 30, 2018	Nov. 30, 2019	Nov. 30, 2018	Aug. 31, 2019	May 31, 2019	Aug. 31, 2018	May 31, 2018
Stockholder's Equity [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (82)	$ 832	$ (82)	$ 832	$ (114)	$ (147)	$ (214)	$ 8,544
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(32)	(11)
Cumulative effect from adoption of new accounting standard				(8,794)
Other Comprehensive Income Loss Reclassification Adjustment From AOCI Foreclosed Asset			65	23
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent		1,046		1,082
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, after Tax		1,035		1,059
Accumulated Net Investment Gain (Loss) Attributable to Parent
Stockholder's Equity [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	0	0	0	0	0	0	0	8,794
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent		0		0
AOCI, Derivative Qualifying as Hedge, Excluded Component, Parent [Member]
Stockholder's Equity [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	2,345	2,800	2,345	2,800	2,459	2,571	2,920	3,039
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	114	120
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax			(226)	(239)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent		(120)		(239)
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent
Stockholder's Equity [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	0	0	0	0	0	0	(1,035)	(1,059)
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax		1,035		1,059
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax		0	0	0
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent		1,035		1,059
Accumulated Defined Benefit Plans Adjustment, Net Transition Attributable to Parent
Stockholder's Equity [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(2,427)	(1,968)	(2,427)	(1,968)	$ (2,573)	$ (2,718)	$ (2,099)	$ (2,230)
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	$ 146	131	$ 291	262
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent		$ 131		262
Retained Earnings, Unappropriated
Stockholder's Equity [Line Items]
Cumulative effect from adoption of new accounting standard				$ (8,794)