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		9 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2017
Segment Reporting Information [Line Items]
Other acquired intangible assets, net	$ 33,862		$ 33,862		$ 41,677
Goodwill	120,682		120,682		119,876
Amortization of acquired intangible assets	3,177	$ 2,775	9,757	$ 7,565
Operating Segments [Member] | Satellite Services [Member]
Segment Reporting Information [Line Items]
Other acquired intangible assets, net	17,449		17,449		21,843
Goodwill	13,876		13,876		13,579
Amortization of acquired intangible assets	2,031	1,605	6,297	3,814
Operating Segments [Member] | Commercial Networks [Member]
Segment Reporting Information [Line Items]
Other acquired intangible assets, net	3,725		3,725		4,903
Goodwill	43,969		43,969		43,930
Amortization of acquired intangible assets	385	411	1,178	1,267
Operating Segments [Member] | Government Systems [Member]
Segment Reporting Information [Line Items]
Other acquired intangible assets, net	12,688		12,688		14,931
Goodwill	62,837		62,837		$ 62,367
Amortization of acquired intangible assets	$ 761	$ 759	$ 2,282	$ 2,484