Segment Information - Segment Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Mar. 31, 2020
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 5,203,396	$ 4,883,868
Operating Segments [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	715,969	758,758
Operating Segments [Member] | Satellite Services [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	57,784	86,252
Operating Segments [Member] | Commercial Networks [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	183,063	188,269
Operating Segments [Member] | Government Systems [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	475,122	484,237
Corporate, Non-Segment [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 4,487,427	$ 4,125,110