INCOME TAXES: Effective Income Tax Rate Reconciliation (Details 2)	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Income Tax Disclosure [Abstract]
Statutory federal income tax rate	30.80%	34.00%	34.00%
State and local income tax rate	2.50%	1.50%	1.50%
Revaluation of net deferred tax assets due to Tax Act	11.40%	0.00%	0.00%
ESOP market value adjustment	(0.00%)	(0.10%)	(0.10%)
BOLI	(1.50%)	(3.80%)	(2.80%)
Other, net	(0.10%)	(0.20%)	2.20%
Effective federal income tax rate	43.10%	31.40%	34.80%