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Senior Notes and Other Long-Term Debt - Additional Information (Detail)	3 Months Ended	6 Months Ended		12 Months Ended
	Jun. 30, 2019 USD ($)	Sep. 30, 2019 USD ($) Installment	Sep. 30, 2018 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2017 USD ($)
Debt Instrument [Line Items]
Proceeds from insurance claims on ViaSat-2 satellite	$ 2,300,000	$ 2,277,000	$ 44,394,000	$ 185,700,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Credit Facility maximum borrowing capacity		$ 700,000,000.0
Maturity date of the Credit Facility		Jan. 18, 2024
Principal amount of outstanding borrowings under the Credit Facility		$ 0
Borrowing availability under the Credit Facility		$ 681,100,000
Credit Facility interest rate description		Borrowings under the Revolving Credit Facility bear interest, at the Company’s option, at either (1) the highest of the Federal Funds rate plus 0.50%, the Eurodollar rate plus 1.00%, or the administrative agent’s prime rate as announced from time to time, or (2) the Eurodollar rate, plus, in the case of each of (1) and (2), an applicable margin that is based on the Company’s total leverage ratio.
Credit facility description		The Revolving Credit Facility contains financial covenants regarding a maximum total leverage ratio and a minimum interest coverage ratio. In addition, the Revolving Credit Facility contains covenants that restrict, among other things, the Company’s ability to sell assets, make investments and acquisitions, make capital expenditures, grant liens, pay dividends and make certain other restricted payments.
Ex-Im Credit Facility [Member]
Debt Instrument [Line Items]
Credit Facility maximum borrowing capacity		$ 362,400,000
Principal amount of outstanding borrowings under the Credit Facility		$ 127,700,000
Credit facility description		The Ex-Im Credit Facility contains financial covenants regarding Viasat’s maximum total leverage ratio and minimum interest coverage ratio. In addition, the Ex-Im Credit Facility contains covenants that restrict, among other things, the Company’s ability to sell assets, make investments and acquisitions, make capital expenditures, grant liens, pay dividends and make certain other restricted payments.
Amount of qualified ViaSat-2 satellite costs limited to finance		$ 321,200,000
Percent of qualified ViaSat-2 expenses used to finance		85.00%
The maximum exposure fees under Ex-Im Credit Facility		$ 41,200,000
Interest rate on the outstanding borrowings		2.38%
Required number of installment repayments \| Installment		16
Debt maturity date		Oct. 15, 2025
Effective interest rate on the Ex-Im Credit Facility		4.54%
Ex-Im credit facility repayment commenced date		Apr. 15, 2018
Cumulative Ex-Im Credit Facility loan discount		$ 42,300,000
Exposure fees included in the principal		35,300,000
The exposure fees paid under Ex-Im Credit Facility borrowings		$ 6,000,000.0
2027 Notes [Member]
Debt Instrument [Line Items]
Interest rate on the outstanding borrowings		5.625%
Debt maturity date		Apr. 15, 2027
Principal amount of senior notes issued		$ 600,000,000.0		$ 600,000,000.0
2027 Notes [Member] \| Debt Instrument, Redemption, Other Period One [Member]
Debt Instrument [Line Items]
Redemption price percentage of Senior Notes		105.625%
Redemption description of Senior Notes		Prior to April 15, 2022, the Company may redeem up to 40% of the 2027 Notes at a redemption price of 105.625% of the principal amount thereof, plus accrued and unpaid interest, if any, thereon to the redemption date, from the net cash proceeds of specified equity offerings.
2027 Notes [Member] \| Debt Instrument, Redemption, Period One [Member]
Debt Instrument [Line Items]
Redemption price percentage of Senior Notes		100.00%
Redemption description of Senior Notes		The Company may also redeem the 2027 Notes prior to April 15, 2022, in whole or in part, at a redemption price equal to 100% of the principal amount thereof plus the applicable premium and any accrued and unpaid interest, if any, thereon to the redemption date. The applicable premium is calculated as the greater of: (i) 1.0% of the principal amount of such 2027 Notes and (ii) the excess, if any, of (a) the present value at such date of redemption of (1) the redemption price of such 2027 Notes on April 15, 2022 plus (2) all required interest payments due on such 2027 Notes through April 15, 2022 (excluding accrued but unpaid interest to the date of redemption), computed using a discount rate equal to the treasury rate (as defined under the indenture governing the 2027 Notes) plus 50 basis points, over (b) the then-outstanding principal amount of such 2027 Notes.
2027 Notes [Member] \| Debt Instrument, Redemption, Period Two [Member]
Debt Instrument [Line Items]
Redemption price percentage of Senior Notes		102.813%
Redemption description of Senior Notes		in whole or in part, at any time during the 12 months beginning on April 15, 2022 at a redemption price of 102.813%
2027 Notes [Member] \| Debt Instrument, Redemption, Period Four [Member]
Debt Instrument [Line Items]
Redemption price percentage of Senior Notes		100.00%
Redemption description of Senior Notes		at any time on or after April 15, 2024 at a redemption price of 100%, in each case plus accrued and unpaid interest, if any, thereon to the redemption date.
2027 Notes [Member] \| Debt Instrument, Redemption, Period Three [Member]
Debt Instrument [Line Items]
Redemption price percentage of Senior Notes		101.406%
Redemption description of Senior Notes		during the 12 months beginning on April 15, 2023 at a redemption price of 101.406%
2027 Notes [Member] \| Change of Control [Member]
Debt Instrument [Line Items]
Redemption price percentage of Senior Notes		101.00%
Redemption description of Senior Notes		In the event a change of control triggering event occurs (as defined in the indenture governing the 2027 Notes), each holder will have the right to require the Company to repurchase all or any part of such holder’s 2027 Notes at a purchase price in cash equal to 101% of the aggregate principal amount of the 2027 Notes repurchased, plus accrued and unpaid interest, if any, to the date of purchase (subject to the right of holders of record on the relevant record date to receive interest due on the relevant interest payment date).
2025 Notes [Member]
Debt Instrument [Line Items]
Interest rate on the outstanding borrowings		5.625%
Debt maturity date		Sep. 15, 2025
Principal amount of senior notes issued		$ 700,000,000.0			$ 700,000,000.0
2025 Notes [Member] \| Debt Instrument, Redemption, Other Period One [Member]
Debt Instrument [Line Items]
Redemption price percentage of Senior Notes		105.625%
Redemption description of Senior Notes		Prior to September 15, 2020, the Company may redeem up to 40% of the 2025 Notes at a redemption price of 105.625% of the principal amount thereof, plus accrued and unpaid interest, if any, thereon to the redemption date, from the net cash proceeds of specified equity offerings.
2025 Notes [Member] \| Debt Instrument, Redemption, Period One [Member]
Debt Instrument [Line Items]
Redemption price percentage of Senior Notes		100.00%
Redemption description of Senior Notes		The Company may also redeem the 2025 Notes prior to September 15, 2020, in whole or in part, at a redemption price equal to 100% of the principal amount thereof plus the applicable premium and any accrued and unpaid interest, if any, thereon to the redemption date. The applicable premium is calculated as the greater of: (i) 1.0% of the principal amount of such 2025 Notes and (ii) the excess, if any, of (a) the present value at such date of redemption of (1) the redemption price of such 2025 Notes on September 15, 2020 plus (2) all required interest payments due on such 2025 Notes through September 15, 2020 (excluding accrued but unpaid interest to the date of redemption), computed using a discount rate equal to the treasury rate (as defined under the indenture governing the 2025 Notes) plus 50 basis points, over (b) the then-outstanding principal amount of such 2025 Notes.
2025 Notes [Member] \| Debt Instrument, Redemption, Period Two [Member]
Debt Instrument [Line Items]
Redemption price percentage of Senior Notes		102.813%
Redemption description of Senior Notes		in whole or in part, at any time during the 12 months beginning on September 15, 2020 at a redemption price of 102.813%
2025 Notes [Member] \| Debt Instrument, Redemption, Period Four [Member]
Debt Instrument [Line Items]
Redemption price percentage of Senior Notes		100.00%
Redemption description of Senior Notes		at any time on or after September 15, 2022 at a redemption price of 100%, in each case plus accrued and unpaid interest, if any, thereon to the redemption date.
2025 Notes [Member] \| Debt Instrument, Redemption, Period Three [Member]
Debt Instrument [Line Items]
Redemption price percentage of Senior Notes		101.406%
Redemption description of Senior Notes		during the 12 months beginning on September 15, 2021 at a redemption price of 101.406%
2025 Notes [Member] \| Change of Control [Member]
Debt Instrument [Line Items]
Redemption price percentage of Senior Notes		101.00%
Redemption description of Senior Notes		In the event a change of control triggering event occurs (as defined in the indenture governing the 2025 Notes), each holder will have the right to require the Company to repurchase all or any part of such holder’s 2025 Notes at a purchase price in cash equal to 101% of the aggregate principal amount of the 2025 Notes repurchased, plus accrued and unpaid interest, if any, to the date of purchase (subject to the right of holders of record on the relevant record date to receive interest due on the relevant interest payment date).
Letter of Credit [Member]
Debt Instrument [Line Items]
Credit Facility maximum borrowing capacity		$ 150,000,000.0
Standby letters of credit outstanding amount		$ 18,900,000