Segment Information - Segment Revenues and Operating Profits (Losses) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Revenues:
Total revenues	$ 554,694	$ 381,837	$ 1,511,037	$ 1,154,955
Operating profits (losses):
Income (loss) from operations	6,007	(25,326)	(70,043)	(59,136)
Amortization of acquired intangible assets	(2,487)	(3,177)	(7,375)	(9,757)
Product [Member]
Revenues:
Total revenues	301,865	175,957	800,429	523,858
Service [Member]
Revenues:
Total revenues	252,829	205,880	710,608	631,097
Operating Segments [Member]
Operating profits (losses):
Income (loss) from operations	8,494	(22,149)	(62,668)	(49,379)
Operating Segments [Member] | Satellite Services [Member]
Revenues:
Total revenues	177,651	144,543	494,174	444,335
Operating profits (losses):
Income (loss) from operations	(10,196)	1,681	(64,971)	33,140
Amortization of acquired intangible assets	(1,183)	(2,031)	(3,776)	(6,297)
Operating Segments [Member] | Satellite Services [Member] | Product [Member]
Revenues:
Total revenues		233		664
Operating Segments [Member] | Satellite Services [Member] | Service [Member]
Revenues:
Total revenues	177,651	144,310	494,174	443,671
Operating Segments [Member] | Commercial Networks [Member]
Revenues:
Total revenues	126,977	55,536	336,563	157,053
Operating profits (losses):
Income (loss) from operations	(31,219)	(53,505)	(117,424)	(179,007)
Amortization of acquired intangible assets	(386)	(385)	(1,157)	(1,178)
Operating Segments [Member] | Commercial Networks [Member] | Product [Member]
Revenues:
Total revenues	115,409	47,073	304,732	130,903
Operating Segments [Member] | Commercial Networks [Member] | Service [Member]
Revenues:
Total revenues	11,568	8,463	31,831	26,150
Operating Segments [Member] | Government Systems [Member]
Revenues:
Total revenues	250,066	181,758	680,300	553,567
Operating profits (losses):
Income (loss) from operations	49,909	29,675	119,727	96,488
Amortization of acquired intangible assets	(918)	(761)	(2,442)	(2,282)
Operating Segments [Member] | Government Systems [Member] | Product [Member]
Revenues:
Total revenues	186,456	128,651	495,697	392,291
Operating Segments [Member] | Government Systems [Member] | Service [Member]
Revenues:
Total revenues	63,610	53,107	184,603	161,276
Material Reconciling Items [Member]
Operating profits (losses):
Amortization of acquired intangible assets	$ (2,487)	$ (3,177)	$ (7,375)	$ (9,757)