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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2018
Segment Reporting Information [Line Items]
Other acquired intangible assets, net	$ 26,072		$ 26,072		$ 31,862
Goodwill	122,676		122,676		121,085
Amortization of acquired intangible assets	2,435	$ 3,320	4,888	$ 6,580
Operating Segments [Member] | Satellite Services [Member]
Segment Reporting Information [Line Items]
Other acquired intangible assets, net	13,112		13,112		16,580
Goodwill	13,749		13,749		13,991
Amortization of acquired intangible assets	1,289	2,173	2,593	4,267
Operating Segments [Member] | Commercial Networks [Member]
Segment Reporting Information [Line Items]
Other acquired intangible assets, net	2,569		2,569		3,340
Goodwill	43,959		43,959		44,011
Amortization of acquired intangible assets	385	386	771	792
Operating Segments [Member] | Government Systems [Member]
Segment Reporting Information [Line Items]
Other acquired intangible assets, net	10,391		10,391		11,942
Goodwill	64,968		64,968		$ 63,083
Amortization of acquired intangible assets	$ 761	$ 761	$ 1,524	$ 1,521