Segment Information - Segment Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Mar. 31, 2020
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 5,248,706	$ 4,883,868
Operating Segments [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	667,446	758,758
Operating Segments [Member] | Satellite Services [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	57,706	86,252
Operating Segments [Member] | Commercial Networks [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	169,946	188,269
Operating Segments [Member] | Government Systems [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	439,794	484,237
Corporate, Non-Segment [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 4,581,260	$ 4,125,110