Segment Information - Segment Assets (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 3,414,109	$ 2,954,653	$ 2,397,312
Operating Segments [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	615,728	587,962	582,399
Operating Segments [Member] | Satellite Services [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	66,830	81,728	57,529
Operating Segments [Member] | Commercial Networks [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	211,447	179,992	212,943
Operating Segments [Member] | Government Systems [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	337,451	326,242	311,927
Corporate, Non-Segment [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 2,798,381	$ 2,366,691	$ 1,814,913