Schedule II - Valuation and Qualifying Accounts (Detail) - Allowance for Doubtful Accounts [Member] - USD ($)	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Valuation And Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	$ 3,001,000	$ 1,821,000	$ 1,645,000
Additions Charged to Cost and Expenses	2,559,000	2,335,000	1,357,000
Deductions	(1,009,000)	(1,155,000)	(1,181,000)
Balance at End of Year	$ 4,551,000	$ 3,001,000	$ 1,821,000