Segment Information - Segment Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Mar. 31, 2017
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 3,288,221	$ 2,954,653
Operating Segments [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	589,264	587,962
Operating Segments [Member] | Satellite Services [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	74,234	81,728
Operating Segments [Member] | Commercial Networks [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	192,563	179,992
Operating Segments [Member] | Government Systems [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	322,467	326,242
Corporate, Non-Segment [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 2,698,957	$ 2,366,691