Equity Method Investments and Related-Party Transactions - Schedule of Related Party Transactions (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2018
Euro Infrastructure Co [Member]
Related Party Transaction [Line Items]
Revenue	$ 1,327	$ 2,177	$ 3,178	$ 5,628
Expense	2,432	1,757	4,590	3,588
Cash received	3,624	2,278	6,054	4,349
Cash paid	2,145	$ 1,989	4,092	$ 4,009
Accounts receivable					$ 3,307
Collections in excess of revenues and deferred revenues	4,007		4,007		3,246
Accounts payable	1,379		1,379
Ducommun Inc. [Member]
Related Party Transaction [Line Items]
Cash paid	4,521		6,979
Accounts payable	$ 6,684		$ 6,684		$ 2,073

Amount for accounts payable to related parties.

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