Segment Information - Segment Assets (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Mar. 31, 2018
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 3,544,268	$ 3,414,109
Operating Segments [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	607,461	615,728
Operating Segments [Member] | Satellite Services [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	73,919	66,830
Operating Segments [Member] | Commercial Networks [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	214,942	211,447
Operating Segments [Member] | Government Systems [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	318,600	337,451
Corporate, Non-Segment [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 2,936,807	$ 2,798,381