Pension and Other Post-retirement Benefit Plans - Amounts in Financial Statements (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Accumulated Other Comprehensive Income (Loss) Tax	$ 2,700	$ 2,000
Pension
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Future Amortization of Gain (Loss)	362
Amounts recognized in the Consolidated Balance Sheets
Current liability	(827)	(833)
Noncurrent liability	(34,340)	(34,615)
Amount recognized, end of year	(35,167)	(35,448)
Accumulated other comprehensive income (loss)
Net actuarial loss (gain)	16,196	15,585
Prior service cost	1,500	1,582
Accumulated other comprehensive (income) loss	17,696	17,167
Components of benefit costs (credit)
Net service cost	1,298	1,507	$ 1,286
Interest cost	1,297	1,347	1,819
Expected return on plan assets	(346)	(433)	(499)
Amortization:
Actuarial (gain) loss	419	704	277
Prior service cost	82	60	17
One time expense (income)	(11)	0	0
Net periodic benefit cost (credit)	2,739	3,185	2,900
Defined Benefit Plan, Future Amortization of Prior Service Cost (Credit)	80
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Future Amortization of Gain (Loss)	188
Amounts recognized in the Consolidated Balance Sheets
Current liability	(52)	(82)
Noncurrent liability	(334)	(541)
Amount recognized, end of year	(386)	(623)
Accumulated other comprehensive income (loss)
Net actuarial loss (gain)	(1,134)	(1,114)
Prior service cost	0	0
Accumulated other comprehensive (income) loss	(1,134)	(1,114)
Components of benefit costs (credit)
Net service cost	0	0	0
Interest cost	11	19	29
Expected return on plan assets	0	0	0
Amortization:
Actuarial (gain) loss	(207)	(191)	(187)
Prior service cost	0	0	0
One time expense (income)	0	0	0
Net periodic benefit cost (credit)	$ (196)	$ (172)	$ (158)