Composition of Certain Balance Sheet Captions - Composition of Certain Balance Sheet Captions (Parenthetical) (Detail)	9 Months Ended
	Dec. 31, 2017
Minimum [Member]
Schedule Of Composition Of Certain Balance Sheet Captions [Line Items]
Property, equipment and satellites, estimated useful life (years)	2 years
Maximum [Member]
Schedule Of Composition Of Certain Balance Sheet Captions [Line Items]
Property, equipment and satellites, estimated useful life (years)	24 years
Satellites [Member] | Minimum [Member]
Schedule Of Composition Of Certain Balance Sheet Captions [Line Items]
Property, equipment and satellites, estimated useful life (years)	10 years
Satellites [Member] | Maximum [Member]
Schedule Of Composition Of Certain Balance Sheet Captions [Line Items]
Property, equipment and satellites, estimated useful life (years)	17 years
Capital Lease of Satellite Capacity - Anik F2 [Member]
Schedule Of Composition Of Certain Balance Sheet Captions [Line Items]
Property, equipment and satellites, estimated useful life (years)	10 years
Equipment and Software [Member] | Minimum [Member]
Schedule Of Composition Of Certain Balance Sheet Captions [Line Items]
Property, equipment and satellites, estimated useful life (years)	2 years
Equipment and Software [Member] | Maximum [Member]
Schedule Of Composition Of Certain Balance Sheet Captions [Line Items]
Property, equipment and satellites, estimated useful life (years)	7 years
CPE Leased Equipment [Member] | Minimum [Member]
Schedule Of Composition Of Certain Balance Sheet Captions [Line Items]
Property, equipment and satellites, estimated useful life (years)	4 years
CPE Leased Equipment [Member] | Maximum [Member]
Schedule Of Composition Of Certain Balance Sheet Captions [Line Items]
Property, equipment and satellites, estimated useful life (years)	5 years
Furniture and Fixtures [Member]
Schedule Of Composition Of Certain Balance Sheet Captions [Line Items]
Property, equipment and satellites, estimated useful life (years)	7 years
Leasehold Improvements [Member] | Minimum [Member]
Schedule Of Composition Of Certain Balance Sheet Captions [Line Items]
Property, equipment and satellites, estimated useful life (years)	2 years
Leasehold Improvements [Member] | Maximum [Member]
Schedule Of Composition Of Certain Balance Sheet Captions [Line Items]
Property, equipment and satellites, estimated useful life (years)	17 years
Building [Member]
Schedule Of Composition Of Certain Balance Sheet Captions [Line Items]
Property, equipment and satellites, estimated useful life (years)	24 years
Technology [Member]
Schedule Of Composition Of Certain Balance Sheet Captions [Line Items]
Other acquired intangible assets, weighted average useful life	6 years
Contracts and Customer Relationships [Member]
Schedule Of Composition Of Certain Balance Sheet Captions [Line Items]
Other acquired intangible assets, weighted average useful life	7 years
Satellite Co-Location Rights [Member]
Schedule Of Composition Of Certain Balance Sheet Captions [Line Items]
Other acquired intangible assets, weighted average useful life	9 years
Trade Name [Member]
Schedule Of Composition Of Certain Balance Sheet Captions [Line Items]
Other acquired intangible assets, weighted average useful life	3 years
Other [Member]
Schedule Of Composition Of Certain Balance Sheet Captions [Line Items]
Other acquired intangible assets, weighted average useful life	6 years