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	Dec. 31, 2017	Mar. 31, 2017
Schedule of Equity Method Investments [Line Items]
Carrying value of investment in Euro Infrastructure Co.	$ 160,975	$ 141,894
Euro Infrastructure Co [Member]
Schedule of Equity Method Investments [Line Items]
Carrying value of investment in Euro Infrastructure Co.	160,975	141,894
Less: proportionate share of net assets of Euro Infrastructure Co.	144,560	127,393
Excess carrying value of investment over proportionate share of net assets	16,415	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	23,171	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	13,059	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	(21,504)	(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	$ 1,689	$ 1,572