Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended
	Jul. 31, 2016	Sep. 30, 2018	Mar. 31, 2018
Unfavorable Regulatory Action [Member]
Long-term Purchase Commitment [Line Items]
U.S. government contract-related reserves		$ 2.6	$ 1.6
ViaSat-3 Class Satellites [Member] | Capital Addition [Member]
Long-term Purchase Commitment [Line Items]
Commitment amount	$ 379.5