Segment Information - Segment Revenues and Operating Profits (Losses) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenues:
Total revenues	$ 592,256	$ 517,474	$ 1,129,293	$ 956,343
Operating profits (losses):
Income (loss) from operations	18,425	(21,571)	10,360	(76,050)
Amortization of acquired intangible assets	(2,027)	(2,435)	(4,064)	(4,888)
Product [Member]
Revenues:
Total revenues	306,830	280,435	570,445	498,564
Service [Member]
Revenues:
Total revenues	285,426	237,039	558,848	457,779
Operating Segments [Member]
Operating profits (losses):
Income (loss) from operations	20,452	(19,136)	14,424	(71,162)
Operating Segments [Member] | Satellite Services [Member]
Revenues:
Total revenues	205,717	162,962	402,532	316,523
Operating profits (losses):
Income (loss) from operations	5,118	(24,839)	3,048	(54,775)
Amortization of acquired intangible assets	(850)	(1,289)	(1,705)	(2,593)
Operating Segments [Member] | Satellite Services [Member] | Service [Member]
Revenues:
Total revenues	205,717	162,962	402,532	316,523
Operating Segments [Member] | Commercial Networks [Member]
Revenues:
Total revenues	88,008	114,520	167,020	209,586
Operating profits (losses):
Income (loss) from operations	(46,781)	(39,197)	(96,642)	(86,205)
Amortization of acquired intangible assets	(386)	(385)	(772)	(771)
Operating Segments [Member] | Commercial Networks [Member] | Product [Member]
Revenues:
Total revenues	74,143	104,190	139,044	189,323
Operating Segments [Member] | Commercial Networks [Member] | Service [Member]
Revenues:
Total revenues	13,865	10,330	27,976	20,263
Operating Segments [Member] | Government Systems [Member]
Revenues:
Total revenues	298,531	239,992	559,741	430,234
Operating profits (losses):
Income (loss) from operations	62,115	44,900	108,018	69,818
Amortization of acquired intangible assets	(791)	(761)	(1,587)	(1,524)
Operating Segments [Member] | Government Systems [Member] | Product [Member]
Revenues:
Total revenues	232,687	176,245	431,401	309,241
Operating Segments [Member] | Government Systems [Member] | Service [Member]
Revenues:
Total revenues	65,844	63,747	128,340	120,993
Material Reconciling Items [Member]
Operating profits (losses):
Amortization of acquired intangible assets	$ (2,027)	$ (2,435)	$ (4,064)	$ (4,888)