BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES, Compensating Balances and Other Investments; Holdbacks (Details) - USD ($)
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9 Months Ended |
Jan. 31, 2016 |
Jan. 31, 2015 |
| Compensating Balances [Line Items] |
|
|
| Compensating balances |
$ 13,160,000
|
|
| Decrease in lender holdbacks |
3,906,000
|
$ 11,063,000
|
| Increase in lender holdbacks |
862,000
|
$ 913,000
|
| First International Bank, Watford City, North Dakota [Member] |
|
|
| Compensating Balances [Line Items] |
|
|
| Compensating balances |
6,000,000
|
|
| Associated Bank, Green Bay, Wisconsin [Member] |
|
|
| Compensating Balances [Line Items] |
|
|
| Compensating balances |
3,000,000
|
|
| Private Bank, Minneapolis, Minnesota [Member] |
|
|
| Compensating Balances [Line Items] |
|
|
| Compensating balances |
2,000,000
|
|
| Bremer Bank, Saint Paul, Minnesota [Member] |
|
|
| Compensating Balances [Line Items] |
|
|
| Compensating balances |
1,285,000
|
|
| Dacotah Bank, Minot, North Dakota [Member] |
|
|
| Compensating Balances [Line Items] |
|
|
| Compensating balances |
$ 350,000
|
|
| Remaining terms of certificates of deposit |
6 months
|
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| Dacotah Bank, Minot, North Dakota [Member] | Other Investments [Member] |
|
|
| Compensating Balances [Line Items] |
|
|
| Certificates of deposit |
$ 50,000
|
|
| Peoples State Bank of Velva, North Dakota [Member] |
|
|
| Compensating Balances [Line Items] |
|
|
| Compensating balances |
225,000
|
|
| American National Bank, Omaha, Nebraska [Member] |
|
|
| Compensating Balances [Line Items] |
|
|
| Compensating balances |
200,000
|
|
| Commerce Bank, a Minnesota Banking Corporation [Member] |
|
|
| Compensating Balances [Line Items] |
|
|
| Compensating balances |
$ 100,000
|
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