Segment Information - Other Acquired Intangible Assets, Net and Goodwill Included in Segment Assets and Amortization of Acquired Intangible Assets by Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Mar. 31, 2017
Segment Reporting Information [Line Items]
Other acquired intangible assets, net	$ 36,796		$ 36,796		$ 41,677
Goodwill	120,592		120,592		119,876
Amortization of acquired intangible assets	3,320	$ 2,277	6,580	$ 4,790
Operating Segments [Member] | Satellite Services [Member]
Segment Reporting Information [Line Items]
Other acquired intangible assets, net	19,238		19,238		21,843
Goodwill	13,814		13,814		13,579
Amortization of acquired intangible assets	2,173	1,105	4,267	2,209
Operating Segments [Member] | Commercial Networks [Member]
Segment Reporting Information [Line Items]
Other acquired intangible assets, net	4,111		4,111		4,903
Goodwill	43,981		43,981		43,930
Amortization of acquired intangible assets	386	411	792	856
Operating Segments [Member] | Government Systems [Member]
Segment Reporting Information [Line Items]
Other acquired intangible assets, net	13,447		13,447		14,931
Goodwill	62,797		62,797		$ 62,367
Amortization of acquired intangible assets	$ 761	$ 761	$ 1,521	$ 1,725