Fair Value Measurements - Additional Information (Detail) € in Millions		6 Months Ended
	Apr. 30, 2021 USD ($)	Sep. 30, 2021 USD ($)	Apr. 30, 2021 EUR (€)	Mar. 31, 2021 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2017 USD ($)
Satellite Performance Incentives Obligation [Member] | ViaSat-1 Satellite [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Expiration year of in-orbit satellite performance incentive obligation		2027
Satellite Performance Incentives Obligation [Member] | ViaSat-2 Satellite [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Expiration year of in-orbit satellite performance incentive obligation		2028
2025 Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Principal amount of senior notes issued		$ 700,000,000.0					$ 700,000,000.0
2027 Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Principal amount of senior notes issued		600,000,000.0				$ 600,000,000.0
2028 Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Principal amount of senior notes issued		$ 400,000,000.0			$ 400,000,000.0
Euro​ Infrastructure​ Co Step Acquisition [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Percentage of additional interest in subsidiary acquired	51.00%		51.00%
Contingent consideration arrangements	the Company may pay or receive up to €20.0 million, or approximately $23.4 million, in cash.	up to plus or minus €20.0 million
Euro​ Infrastructure​ Co Step Acquisition [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value estimate of the maximum amount of the contingency	$ 23,400,000		€ 20.0
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value on a recurring basis		$ 0		$ 0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents measured at fair value on a recurring basis		5,000,000.0		5,000,000.0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Satellite Performance Incentives Obligation [Member] | ViaSat-1 and ViaSat-2 Satellites [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Satellite performance incentives obligation		25,600,000		27,100,000
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | 2025 Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of long term debt		708,100,000		709,600,000
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | 2027 Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of long term debt		624,000,000.0		629,200,000
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | 2028 Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of long term debt		420,300,000		420,500,000
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Ex-Im Credit Facility [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of long term debt		$ 89,500,000		$ 100,100,000