Equity Method Investments and Related-Party Transactions - The Difference Between Carrying Value of Investment in Euro Infrastructure Co. and Proportionate Share of Net Assets of Euro Infrastructure Co. (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Mar. 31, 2019
Schedule of Equity Method Investments [Line Items]
Investment in unconsolidated affiliate	$ 162,096	$ 160,711
Euro Infrastructure Co [Member]
Schedule of Equity Method Investments [Line Items]
Investment in unconsolidated affiliate	162,096	160,711
Less: proportionate share of net assets of Euro Infrastructure Co.	146,400	145,016
Excess carrying value of investment over proportionate share of net assets	15,696	15,695
Euro Infrastructure Co [Member] | Goodwill [Member]
Schedule of Equity Method Investments [Line Items]
Excess carrying value of investment over proportionate share of net assets	22,309	22,476
Euro Infrastructure Co [Member] | Identifiable Intangible Assets [Member]
Schedule of Equity Method Investments [Line Items]
Excess carrying value of investment over proportionate share of net assets	9,806	10,670
Euro Infrastructure Co [Member] | Tangible Assets [Member]
Schedule of Equity Method Investments [Line Items]
Excess carrying value of investment over proportionate share of net assets	(17,463)	(18,522)
Euro Infrastructure Co [Member] | Deferred Income Taxes [Member]
Schedule of Equity Method Investments [Line Items]
Excess carrying value of investment over proportionate share of net assets	$ 1,044	$ 1,071