Segment Information - Segment Revenues and Operating Profits (Losses) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenues:
Total revenues	$ 517,474	$ 393,074	$ 956,343	$ 773,118
Operating profits (losses):
Loss from operations	(21,571)	(15,860)	(76,050)	(33,810)
Amortization of acquired intangible assets	(2,435)	(3,320)	(4,888)	(6,580)
Product [Member]
Revenues:
Total revenues	280,435	181,783	498,564	347,901
Service [Member]
Revenues:
Total revenues	237,039	211,291	457,779	425,217
Operating Segments [Member]
Operating profits (losses):
Loss from operations	(19,136)	(12,540)	(71,162)	(27,230)
Operating Segments [Member] | Satellite Services [Member]
Revenues:
Total revenues	162,962	147,578	316,523	299,792
Operating profits (losses):
Loss from operations	(24,839)	12,616	(54,775)	31,459
Amortization of acquired intangible assets	(1,289)	(2,173)	(2,593)	(4,267)
Operating Segments [Member] | Satellite Services [Member] | Product [Member]
Revenues:
Total revenues		214		431
Operating Segments [Member] | Satellite Services [Member] | Service [Member]
Revenues:
Total revenues	162,962	147,364	316,523	299,361
Operating Segments [Member] | Commercial Networks [Member]
Revenues:
Total revenues	114,520	56,269	209,586	101,517
Operating profits (losses):
Loss from operations	(39,197)	(59,377)	(86,205)	(125,502)
Amortization of acquired intangible assets	(385)	(386)	(771)	(792)
Operating Segments [Member] | Commercial Networks [Member] | Product [Member]
Revenues:
Total revenues	104,190	47,347	189,323	83,830
Operating Segments [Member] | Commercial Networks [Member] | Service [Member]
Revenues:
Total revenues	10,330	8,922	20,263	17,687
Operating Segments [Member] | Government Systems [Member]
Revenues:
Total revenues	239,992	189,227	430,234	371,809
Operating profits (losses):
Loss from operations	44,900	34,221	69,818	66,813
Amortization of acquired intangible assets	(761)	(761)	(1,524)	(1,521)
Operating Segments [Member] | Government Systems [Member] | Product [Member]
Revenues:
Total revenues	176,245	134,222	309,241	263,640
Operating Segments [Member] | Government Systems [Member] | Service [Member]
Revenues:
Total revenues	63,747	55,005	120,993	108,169
Material Reconciling Items [Member]
Operating profits (losses):
Amortization of acquired intangible assets	$ (2,435)	$ (3,320)	$ (4,888)	$ (6,580)