Segment Information - Segment Revenues and Operating Profits (Losses) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues:
Total revenues	$ 554,278	$ 592,256	$ 1,084,766	$ 1,129,293
Operating profits (losses):
Income (loss) from operations	12,683	18,425	7,369	10,360
Amortization of acquired intangible assets	(1,300)	(2,027)	(2,858)	(4,064)
Product [Member]
Revenues:
Total revenues	255,980	306,830	506,614	570,445
Service [Member]
Revenues:
Total revenues	298,298	285,426	578,152	558,848
Operating Segments [Member]
Operating profits (losses):
Income (loss) from operations	13,983	20,452	10,227	14,424
Operating Segments [Member] | Satellite Services [Member]
Revenues:
Total revenues	215,887	205,717	417,871	402,532
Operating profits (losses):
Income (loss) from operations	11,483	5,118	9,626	3,048
Amortization of acquired intangible assets	(546)	(850)	(1,055)	(1,705)
Operating Segments [Member] | Satellite Services [Member] | Service [Member]
Revenues:
Total revenues	215,887	205,717	417,871	402,532
Operating Segments [Member] | Commercial Networks [Member]
Revenues:
Total revenues	78,860	88,008	146,022	167,020
Operating profits (losses):
Income (loss) from operations	(45,363)	(46,781)	(96,757)	(96,642)
Amortization of acquired intangible assets		(386)	(257)	(772)
Operating Segments [Member] | Commercial Networks [Member] | Product [Member]
Revenues:
Total revenues	66,751	74,143	121,870	139,044
Operating Segments [Member] | Commercial Networks [Member] | Service [Member]
Revenues:
Total revenues	12,109	13,865	24,152	27,976
Operating Segments [Member] | Government Systems [Member]
Revenues:
Total revenues	259,531	298,531	520,873	559,741
Operating profits (losses):
Income (loss) from operations	47,863	62,115	97,358	108,018
Amortization of acquired intangible assets	(754)	(791)	(1,546)	(1,587)
Operating Segments [Member] | Government Systems [Member] | Product [Member]
Revenues:
Total revenues	189,229	232,687	384,744	431,401
Operating Segments [Member] | Government Systems [Member] | Service [Member]
Revenues:
Total revenues	70,302	65,844	136,129	128,340
Material Reconciling Items [Member]
Operating profits (losses):
Amortization of acquired intangible assets	$ (1,300)	$ (2,027)	$ (2,858)	$ (4,064)