Investment Securities (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Feb. 29, 2016	Feb. 28, 2015	Feb. 29, 2016	Feb. 28, 2015	May. 31, 2015
Investments
Amortized Cost	$ 80,538		$ 80,538		$ 80,538
Gross Unrealized Gains	4,523		4,523		3,934
Gross Unrealized Losses	0		0		0
Fair Value	85,061		85,061		84,472
Unrealized gains (losses) on available-for-sale investment securities	(2,297)	$ 1,644	589	$ 5,246
Preferred Stock | Federal Agricultural Mortgage Corporation Series A preferred stock
Investments
Amortized Cost	30,000		30,000		30,000
Gross Unrealized Gains	687		687		264
Gross Unrealized Losses	0		0		0
Fair Value	30,687		30,687		30,264
Preferred Stock | Federal Agricultural Mortgage Corporation Series B Preferred Stock
Investments
Amortized Cost	25,000		25,000		25,000
Gross Unrealized Gains	1,920		1,920		1,250
Gross Unrealized Losses	0		0		0
Fair Value	26,920		26,920		26,250
Preferred Stock | Federal Agricultural Mortgage Corporation Series C Preferred Stock
Investments
Amortized Cost	25,000		25,000		25,000
Gross Unrealized Gains	60		60		900
Gross Unrealized Losses	0		0		0
Fair Value	25,060		25,060		25,900
Common Stock | Federal Agricultural Mortgage Corporation Class A common stock
Investments
Amortized Cost	538		538		538
Gross Unrealized Gains	1,856		1,856		1,520
Gross Unrealized Losses	0		0		0
Fair Value	$ 2,394		$ 2,394		$ 2,058