Segment Information - Segment Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Mar. 31, 2018
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 3,629,627	$ 3,414,109
Operating Segments [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	649,442	615,728
Operating Segments [Member] | Satellite Services [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	74,195	66,830
Operating Segments [Member] | Commercial Networks [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	227,197	211,447
Operating Segments [Member] | Government Systems [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	348,050	337,451
Corporate, Non-Segment [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 2,980,185	$ 2,798,381