Note 4 - Investment Securities Available for Sale - Debt Securities By Contractual Maturity (Details) - USD ($)	Sep. 30, 2018	Mar. 31, 2018
Amortized cost, securities available for sale, maturing within one year	$ 2,002,643	$ 2,009,160
Fair value, securities available for sale, maturing within one year	1,998,068	1,995,625
Amortized cost, securities available for sale, maturing over one to five years	1,228,815	1,231,928
Fair value, securities available for sale, maturing over one to five years	1,180,880	1,196,368
Amortized cost, securities available for sale maturing over five to ten years	3,573,299	3,578,827
Fair value, securities available for sale, maturing over five to ten years	3,476,232	3,500,641
Amortized cost, securities available for sale, maturing over ten years	10,318,536	10,368,499
Fair value, securities available for sale, maturing over ten years	9,498,050	9,686,082
Amortized cost of mortgage-backed securities, in monthly installments	55,208,284	61,078,665
Fair value of mortgage-backed securities, in monthly installments	52,709,759	59,025,420
Amortized cost of securities available for sale	72,331,577	78,267,079
Fair value of securities available for sale	$ 68,862,989	$ 75,404,136

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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