PROPERTY AND EQUIPMENT: (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Property and Equipment
Property and equipment, gross	$ 491,266	$ 476,281
Less accumulated depreciation and amortization	334,733	320,307
Property and equipment, net	156,533	155,974
Depreciation expense on property and equipment	43,500	42,900	$ 40,600
Land
Property and Equipment
Property and equipment, gross	5,398	5,398
Buildings and improvements
Property and Equipment
Property and equipment, gross	195,609	189,666
Data processing equipment
Property and Equipment
Property and equipment, gross	262,254	249,131
Office furniture and other equipment
Property and Equipment
Property and equipment, gross	$ 28,005	$ 32,086