Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Mar. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fair value of plan assets	$ 8,723	$ 8,759
Supplemental Executive Retirement Plan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	8,747	8,760
Other pending transactions	(25)
Total fair value of plan assets	8,722	8,760
Supplemental Executive Retirement Plan | Measured At Net Asset Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	1,713	1,720
Total fair value of plan assets	1,713	1,720
Supplemental Executive Retirement Plan | Quoted Prices In Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	6,006	6,023
Other pending transactions	(25)
Total fair value of plan assets	5,981	6,023
Supplemental Executive Retirement Plan | Significant Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	1,028	1,017
Total fair value of plan assets	1,028	1,017
Supplemental Executive Retirement Plan | Equity Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	5,121	5,176
Supplemental Executive Retirement Plan | Equity Securities | Quoted Prices In Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	5,121	5,176
Supplemental Executive Retirement Plan | Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	3,386	3,261
Supplemental Executive Retirement Plan | Debt Securities | Measured At Net Asset Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	1,675	1,648
Supplemental Executive Retirement Plan | Debt Securities | Quoted Prices In Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	853	832
Supplemental Executive Retirement Plan | Debt Securities | Significant Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	858	781
Supplemental Executive Retirement Plan | Cash and Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	240	323
Supplemental Executive Retirement Plan | Cash and Cash Equivalents | Measured At Net Asset Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	38	72
Supplemental Executive Retirement Plan | Cash and Cash Equivalents | Quoted Prices In Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	32	15
Supplemental Executive Retirement Plan | Cash and Cash Equivalents | Significant Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	$ 170	$ 236