Employee Benefit Plans (Components of net periodic post retirement benefit cost) (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Postemployment Benefits [Abstract]
Service cost for benefits earned during the period	$ 1,073	$ 1,026	$ 961
Interest cost on accumulated postretirement benefit	869	814	752
Other components	58	88	35
Net periodic postretirement benefit cost	$ 2,000	$ 1,928	$ 1,748