Retirement Benefit Plans - Additional Information (Details) - USD ($)	12 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Retirement Benefit Plans (Textual) [Abstract]
Retirement benefit plans expense	$ 1,553,000	$ 1,233,000	$ 864,000
Net periodic benefit discount rate	3.75%	4.00%	4.25%
Assumed health care cost trend rates	9.00%
Assumed health care cost trending down ultimate rate	5.00%
Benefit obligation discount rate	4.00%	3.75%
Net periodic pension and postretirement medical costs	$ 26,000	$ 30,000	$ 33,000
Postretirement Medical Plan
Retirement Benefit Plans (Textual) [Abstract]
Other long- term benefit obligation	648,000	730,000	787,000
Net gain (loss) recognized in accumulated other comprehensive loss Net Of Tax	(17,000)
Expected actuarial gain/loss	0
Postretirement Medical Plan \| Accrued other expenses
Retirement Benefit Plans (Textual) [Abstract]
Other long- term benefit obligation	65,000	62,000
Postretirement Medical Plan \| Other long term obligation
Retirement Benefit Plans (Textual) [Abstract]
Other long- term benefit obligation	583,000	668,000
Defined Benefit Pension Plan
Retirement Benefit Plans (Textual) [Abstract]
Other long- term benefit obligation	2,630,000	$ 3,883,000	$ 4,027,000
Net gain (loss) recognized in accumulated other comprehensive loss Net Of Tax	$ 161,000
Net periodic benefit discount rate	2.60%	2.70%
Benefit obligation discount rate	2.30%	2.60%
Net pension assets	$ 873,000	$ 570,000
Net gain in AOCI	431,000	$ 304,000
Prior service cost in AOCI	35,000
Transition asset or obligation in AOCI	$ 0
Estimated long term rate of return	3.80%	3.80%
Expected contributions in fiscal 2020	$ 65,000

Retirement Benefit Plans (Textual) [Abstract]

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Amount, after tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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Amount, after tax, of accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

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Amount, after tax, of accumulated other comprehensive (income) loss for cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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Amount, after tax, of accumulated other comprehensive income (loss) for transition asset (obligation) of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

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Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan.

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Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan.

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Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan.

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Amount of actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

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Amount included in accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan expected to be recognized in net periodic benefit (cost) credit for fiscal year following most recent annual statement of financial position.

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Amount of contributions expected to be received by defined benefit plan from employer in next fiscal year following latest fiscal year.

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Amount of funded (unfunded) status of defined benefit plan, measured as difference between fair value of plan assets and benefit obligation. Includes, but is not limited to, overfunded (underfunded) status.

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Assumed rate, for next fiscal year, based on annual change in cost of health care cost benefits used to measure expected cost of benefits covered by defined benefit postretirement plan. Factors include, but are not limited to, estimate of health care inflation, change in health care utilization or delivery pattern, technological advances, and change in health status of participant. Excludes factors for change in composition of plan population by age and dependency status.

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Ultimate trend rate for health care cost for defined benefit postretirement plan.

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Amount of cost for defined contribution plan.

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Amount of cost (reversal of cost) for pension and other postretirement benefits.

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