Schedule of Fair Values of Defined Benefit Plans Determined Using Fair Value Hierarchy of Inputs (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plans	$ 36,541	$ 33,412	$ 26,410
Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plans	144	704
Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plans	36,397	32,708
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plans	4,525	16,533
Equity Securities [Member] \| Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plans	4,525	16,533
Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plans	31,516	15,799
Fixed Income Securities [Member] \| Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plans	31,516	15,799
Real Estate Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plans	144	163
Real Estate Funds [Member] \| Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plans	144	163
Commodity Linked Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plans	212	213
Commodity Linked Funds [Member] \| Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plans	212	213
Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plans	144	704
Cash Equivalents [Member] \| Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plans	$ 144	$ 704