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, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2018
Segment Reporting Information [Line Items]
Other acquired intangible assets, net	$ 24,760		$ 24,760		$ 31,862
Goodwill	121,506		121,506		121,085
Amortization of acquired intangible assets	2,487	$ 3,177	7,375	$ 9,757
Operating Segments [Member] | Satellite Services [Member]
Segment Reporting Information [Line Items]
Other acquired intangible assets, net	11,751		11,751		16,580
Goodwill	13,694		13,694		13,991
Amortization of acquired intangible assets	1,183	2,031	3,776	6,297
Operating Segments [Member] | Commercial Networks [Member]
Segment Reporting Information [Line Items]
Other acquired intangible assets, net	2,183		2,183		3,340
Goodwill	43,955		43,955		44,011
Amortization of acquired intangible assets	386	385	1,157	1,178
Operating Segments [Member] | Government Systems [Member]
Segment Reporting Information [Line Items]
Other acquired intangible assets, net	10,826		10,826		11,942
Goodwill	63,857		63,857		$ 63,083
Amortization of acquired intangible assets	$ 918	$ 761	$ 2,442	$ 2,282