Schedule of Fair Values of Defined Benefit Plans Determined Using Fair Value Hierarchy of Inputs (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plans	$ 33,412	$ 26,410	$ 21,424
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plans	16,533	18,375
Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plans	15,799	7,166
Real Estate Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plans	163	147
Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plans	704	258
Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plans	704	258
Fair Value, Inputs, Level 1 | Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plans	704	258
Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plans	32,708	26,152
Fair Value, Inputs, Level 2 | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plans	16,533	18,375
Fair Value, Inputs, Level 2 | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plans	15,799	7,166
Fair Value, Inputs, Level 2 | Real Estate Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plans	163	147
Commodity Linked Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plans	213	464
Commodity Linked Funds [Member] | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of defined benefit plans	$ 213	$ 464