BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES - Compensating Balances and Other Investments Lender Holdbacks (Details) - USD ($)	3 Months Ended
	Jul. 31, 2016	Jul. 31, 2015
Compensating Balances [Line Items]
Compensating balance	$ 13,060,000
Decrease in lender holdbacks	735,000	$ 1,354,000
Increase in lender holdbacks for improvements	346,000	$ 292,000
First International Bank, Watford City, North Dakota [Member]
Compensating Balances [Line Items]
Compensating balance	6,000,000
Associated Bank, Green Bay, Wisconsin [Member]
Compensating Balances [Line Items]
Compensating balance	3,000,000
Private Bank [Member]
Compensating Balances [Line Items]
Compensating balance	2,000,000
Bremer Bank [Member]
Compensating Balances [Line Items]
Compensating balance	1,285,000
Dacotah Bank, Minot, North Dakota [Member]
Compensating Balances [Line Items]
Compensating balance	250,000
Peoples State Bank of Velva, North Dakota [Member]
Compensating Balances [Line Items]
Compensating balance	225,000
American National Bank, Omaha, Nebraska [Member]
Compensating Balances [Line Items]
Compensating balance	200,000
Commerce Bank [Member]
Compensating Balances [Line Items]
Compensating balance	$ 100,000