Pension and Other Post-retirement Benefit Plans - Benefit Schedules (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Number of Fiscal Years	10 years
Target allocation and weighted-average asset allocations
Target Allocation (as a percent)	100.00%
Plan Assets (as a percent)	100.00%
Estimated future pension benefit payments
2015	$ 1,520
2016	1,612
2017	1,666
2018	1,627
2019	1,690
2021- 2025	11,230
Pension
Other changes in plan assets and benefit obligations recognized in Accumulated other comprehensive income
Current year actuarial (gain) loss	1,229	$ (5,125)	$ 12,397
Amortization of actuarial gain (loss)	(619)	(698)	(258)
Current year prior service cost	0	342	1,006
Amortization of prior service cost	(82)	(60)	(17)
Total recognized in other comprehensive income	528	(5,541)	13,128
Total recognized in net periodic benefit cost and other comprehensive income (loss)	3,267	(2,356)	16,028
Estimated future pension benefit payments
2015	1,467
2016	1,562
2017	1,619
2018	1,584
2019	1,651
2021- 2025	11,090
Other Benefits
Other changes in plan assets and benefit obligations recognized in Accumulated other comprehensive income
Current year actuarial (gain) loss	(228)	(146)	118
Amortization of actuarial gain (loss)	208	191	187
Current year prior service cost	0	0	0
Amortization of prior service cost	0	0	0
Total recognized in other comprehensive income	(20)	45	305
Total recognized in net periodic benefit cost and other comprehensive income (loss)	(216)	$ (127)	$ 147
Estimated future pension benefit payments
2015	53
2016	50
2017	47
2018	43
2019	39
2021- 2025	$ 140
Insurance
Target allocation and weighted-average asset allocations
Target Allocation (as a percent)	10.00%
Plan Assets (as a percent)	6.00%
International equities
Target allocation and weighted-average asset allocations
Target Allocation (as a percent)	15.00%
Plan Assets (as a percent)	18.00%
International bonds
Target allocation and weighted-average asset allocations
Target Allocation (as a percent)	60.00%
Plan Assets (as a percent)	63.00%
Other
Target allocation and weighted-average asset allocations
Target Allocation (as a percent)	15.00%
Plan Assets (as a percent)	13.00%