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, 2017	Mar. 31, 2017
Schedule of Equity Method Investments [Line Items]
Carrying value of investment in Euro Infrastructure Co.	$ 153,973	$ 141,894
Euro Infrastructure Co [Member]
Schedule of Equity Method Investments [Line Items]
Carrying value of investment in Euro Infrastructure Co.	153,973	141,894
Less: proportionate share of net assets of Euro Infrastructure Co.	138,313	127,393
Excess carrying value of investment over proportionate share of net assets	15,660	14,501
Euro Infrastructure Co [Member] | Goodwill [Member]
Schedule of Equity Method Investments [Line Items]
Excess carrying value of investment over proportionate share of net assets	22,537	20,791
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	13,815	12,379
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	(22,411)	(20,241)
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	$ 1,719	$ 1,572