Pension and Other Post-retirement Benefit Plans - Amounts in Financial Statements (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Pension
Amounts recognized in the Consolidated Balance Sheets
Current liability	$ (7,000)	$ (827)
Noncurrent liability	(83,182)	(34,340)
Amount recognized, end of year	(90,182)	(35,167)
Accumulated other comprehensive income (loss)
Net actuarial loss (gain)	15,691	16,196
Prior service cost	1,413	1,500
Accumulated other comprehensive (income) loss	17,104	17,696
Components of benefit costs (credit)
Net service cost	4,585	1,298	$ 1,507
Interest cost	1,750	1,297	1,347
Expected return on plan assets (1)	(1,956)	(346)	(433)
Amortization:
Actuarial (gain) loss (2)	393	419	704
Prior service cost	87	82	60
Recurring activity	4,859	2,750	3,185
One time expense (income)	(71)	(11)	0
Net periodic benefit cost (credit)	4,788	2,739	3,185
Other Benefits
Amounts recognized in the Consolidated Balance Sheets
Current liability	(54)	(52)
Noncurrent liability	(313)	(334)
Amount recognized, end of year	(367)	(386)
Accumulated other comprehensive income (loss)
Net actuarial loss (gain)	(879)	(1,134)
Prior service cost	0	0
Accumulated other comprehensive (income) loss	(879)	(1,134)
Components of benefit costs (credit)
Net service cost	0	0	0
Interest cost	12	11	19
Expected return on plan assets (1)	0	0	0
Amortization:
Actuarial (gain) loss (2)	(191)	(207)	(191)
Prior service cost	0	0	0
Recurring activity	(179)	(196)	(172)
One time expense (income)	0	0	0
Net periodic benefit cost (credit)	$ (179)	$ (196)	$ (172)