Basis of Presentation - Additional Information (Detail)	3 Months Ended				6 Months Ended		12 Months Ended
	Sep. 30, 2019 USD ($) shares	Jun. 30, 2019 USD ($)	Dec. 31, 2018	Sep. 30, 2018 USD ($) shares	Sep. 30, 2019 USD ($) Segment shares	Sep. 30, 2018 USD ($) shares	Mar. 31, 2019 USD ($) shares
Company And Summary Of Significant Accounting Policies [Line Items]
Revenue, practical expedient, financing component					true
Remaining performance obligations	$ 1,900,000,000				$ 1,900,000,000
Number of reportable segments | Segment					3
Increase in unbilled accounts receivable					$ 13,900,000
Decrease in collections in excess of revenues and deferred revenues					17,700,000
Collections in excess of revenues and deferred revenues, recognized revenue	18,600,000			$ 31,500,000	71,200,000	$ 82,100,000
Capitalized interest expense	13,000,000.0			7,500,000	24,300,000	13,700,000
Property, equipment and satellites	3,769,176,000				3,769,176,000		$ 3,419,456,000
Accumulated depreciation and amortization	1,405,260,000				1,405,260,000		1,294,166,000
Proceeds from insurance claims on ViaSat-2 satellite		$ 2,300,000			$ 2,277,000	44,394,000	185,700,000
Lease, practical expedients, package [true false]					true
Total capitalized costs related to patents	3,300,000				$ 3,300,000		3,200,000
Total capitalized costs related to orbital slots and other licenses	34,500,000				34,500,000		22,900,000
Accumulated amortization of patents, orbital slots and other licenses	3,400,000				3,400,000		3,000,000.0
Debt issuance costs capitalized					0	0
Capitalized costs, net, related to software developed for resale	242,273,000				242,273,000		244,368,000
Capitalized cost related to software development for resale	13,900,000			9,600,000	23,600,000	21,000,000.0
Amortization expense of capitalized software development costs	13,700,000			11,700,000	25,700,000	23,100,000
Self-insurance liability	5,600,000				5,600,000		5,400,000
Repurchase and immediate retirement of treasury shares pursuant to vesting of certain RSU agreements	800,000			582,000	3,128,000	2,123,000
Stock-based compensation expense	21,100,000			19,400,000	$ 42,328,000	38,503,000
Accounting Standards Update 2016-02 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements					In February 2016, the Financial Accounting Standards Board (FASB) issued ASU 2016-02, Leases (ASC 842). ASU 2016-02 requires lessees to recognize most leases on their balance sheets as lease liabilities with corresponding right-of-use assets and eliminates certain real estate-specific provisions. In January 2018, the FASB issued ASU 2018-01, Leases (ASC 842). ASU 2018-01 permits an entity to elect an optional transition practical expedient to not evaluate land easements that exist or expired before the entity’s adoption of ASC 842 and that were not previously accounted for as leases under ASC 840. In July 2018, the FASB issued ASU 2018-10, Codification Improvements to ASC 842, Leases, which was issued to provide more detailed guidance and additional clarification for implementing ASU 2016-02. In July 2018, the FASB issued ASU 2018-11, Leases (ASC 842): Targeted Improvements, which provides an additional (and optional) transition method whereby the new lease standard is applied at the adoption date and recognized as an adjustment to retained earnings. In December 2018, the FASB issued ASU 2018-20, Leases (ASC 842): Narrow-Scope Improvements for Lessors, and in March 2019, the FASB issued ASU 2019-01 (ASC 842): Codification Improvements, both of which provide certain amendments that affect narrow aspects of the guidance issued in ASU 2016-02. The new guidance became effective for the Company beginning in the first quarter of fiscal year 2020. The Company adopted the new guidance using the optional transition method in the first quarter of fiscal year 2020. Therefore, the periods prior to the effective date of adoption continue to be reported under the current authoritative guidance for leases (ASC 840). The adoption of this guidance materially impacted the Company’s consolidated balance sheet upon adoption due to the recognition of lease liabilities and right-of-use assets. The new guidance did not have a material impact on the Company’s condensed consolidated statements of operations and comprehensive income (loss) or condensed consolidated statements of cash flows.
Accounting Standards Update 2016-13 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements					In June 2016, the FASB issued ASU 2016-13, Financial Instruments — Credit Losses (ASC 326). ASU 2016-13 requires credit losses on most financial assets measured at amortized cost and certain other instruments to be measured using an expected credit loss model (referred to as the current expected credit loss (CECL) model). It also modifies the impairment model for available-for-sale debt securities and provides for a simplified accounting model for purchased financial assets with credit deterioration since their origination. In November 2018, the FASB issued ASU 2018-19, Codification Improvements to Topic 326, Financial Instruments – Credit Losses (ASC 326), which clarifies that impairment of receivables arising from operating leases should be accounted for in accordance with ASC 842, Leases. In April 2019 the FASB issued ASU 2019-04, Codification Improvements to Topic 326, Financial Instruments – Credit Losses, and in May 2019, the FASB issued ASU 2019-05, Financial Instruments — Credit Losses (ASC 326) Targeted Relief. These recently issued ASUs do not change the core principle of the guidance in ASU 2016-13 but rather are intended to clarify and improve operability of certain topics included within ASU 2016-13. ASU 2018-19, ASU 2019-04 and 2019-05 have the same effective date and transition requirements as ASU 2016-13. The new guidance will become effective for the Company beginning in fiscal year 2021, with early adoption permitted. The new guidance is required to be applied on a modified-retrospective basis. The Company is currently evaluating the impact of this standard on its consolidated financial statements and disclosures.
Accounting Standards Update 2017-04 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements					In January 2017, the FASB issued ASU 2017-04, Intangibles — Goodwill and Other: Simplifying the Test for Goodwill Impairment (ASC 350). ASU 2017-04 removes Step 2 from the goodwill impairment test. The standard will become effective for the Company beginning in fiscal year 2021, with early adoption permitted. The Company is currently evaluating the impact of this standard on its consolidated financial statements and disclosures.
Accounting Standards Update 2017-08 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements					In March 2017, the FASB issued ASU 2017-08, Receivables — Nonrefundable Fees and Other Costs (ASC 310-20): Premium Amortization on Purchased Callable Debt Securities. ASU 2017-08 amends the amortization period for certain callable debt securities held at a premium. The amendments require the premium to be amortized to the earliest call date. The standard became effective for the Company beginning in fiscal year 2020. The Company adopted this guidance beginning in the first quarter of fiscal year 2020 and the guidance did not have a material impact on the Company’s consolidated financial statements and disclosures.
Accounting Standards Update 2017-12 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements					In August 2017, the FASB issued ASU 2017-12, Derivatives and Hedging (ASC 815): Targeted Improvements to Accounting for Hedging Activities. ASU 2017-12 improves the financial reporting of hedging relationships to better portray the economic results of an entity’s risk management activities in its financial statements and make certain targeted improvements to simplify the application of the hedge accounting guidance in current GAAP. The amendments in this update better align an entity’s risk management activities and financial reporting for hedging relationships through changes to both the designation and measurement guidance for qualifying hedging relationships and presentation of hedge results. In October 2018, the FASB issued ASU 2018-16, Derivatives and Hedging (ASC 815): Inclusion of the Secured Overnight Financing Rate (SOFR) Overnight Index SWAP (OIS) Rate as a Benchmark Interest Rate for Hedge Accounting Purposes, which permits use of the OIS rate based on SOFR as a U.S. benchmark interest rate for hedge accounting purposes and has the same effective date as ASU 2017-12. In April 2019, the FASB issued ASU 2019-04, Codification Improvements to Topic 815, Derivatives and Hedging, which clarifies certain aspects of ASC 815 and has the same effective date as ASU 2017-12. The Company adopted this guidance beginning in the first quarter of fiscal year 2020 and the guidance did not have a material impact on the Company’s consolidated financial statements and disclosures.
Accounting Standards Update 2018-09 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements					In July 2018, the FASB issued ASU 2018-09, Codification Improvements, which is related to a project by the FASB to facilitate codification updates for technical corrections, clarifications and other minor improvements. The new standard contains amendments that affect a wide variety of topics in the ASC. The effective date of the standard is dependent on the facts and circumstances of each amendment. Some amendments do not require transition guidance and were effective upon the issuance of this standard. A majority of the amendments in ASU 2018-09 became effective for the Company beginning in fiscal year 2020. The Company adopted the remainder of the amendments of this guidance in the first quarter of fiscal year 2020 and the guidance did not have a material impact on its consolidated financial statements and disclosures.
Accounting Standards Update 2018-13 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements					In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (ASC 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement, which modifies the disclosure requirements for fair value measurements by removing, modifying, or adding certain disclosures. The new standard will become effective for the Company beginning in fiscal year 2021, with early adoption permitted. The Company is currently evaluating the impact of this standard on its consolidated financial statements and disclosures.
Accounting Standards Update 2019-07 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements					In July 2019, the FASB issued ASU 2019-07, Codification Updates to SEC Sections. ASU 2019-07 modifies the disclosure and presentation requirements of a variety of codification topics by aligning them with the Securities and Exchange Commission’s regulations to eliminate redundancies and simplify the application of the codification. The Company adopted this guidance in the second quarter of fiscal year 2020 and the guidance did not have a material impact on the Company’s consolidated financial statements and disclosures.
Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedging [Member] | Foreign Currency Forward Contracts [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Notional value of foreign currency forward contracts outstanding	3,500,000				$ 3,500,000		$ 9,900,000
Foreign currency forward contracts maturity, maximum					21 months
Gains or losses from ineffectiveness of derivative instruments	$ 0			$ 0	$ 0	$ 0
Common Stock Held in Treasury [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Shares of common stock outstanding | shares	0				0		0
Purchase of treasury shares pursuant to vesting of certain RSU agreements | shares	10,269			9,137	36,132	103,337
Repurchase and immediate retirement of treasury shares pursuant to vesting of certain RSU agreements					$ 3,100,000	$ 6,600,000
Common Stock [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Common stock issued based on the vesting terms of certain restricted stock unit agreements | shares	43,290			37,946	115,483	308,731
CPE Leased Equipment [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Property, equipment and satellites	$ 383,858,000				$ 383,858,000		$ 373,357,000
Accumulated depreciation and amortization	154,500,000				154,500,000		142,600,000
Satellites [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Property, equipment and satellites	$ 978,113,000				$ 978,113,000		978,118,000
Reduction in property and equipment, net				$ 177,400,000
ViaSat-2 Satellite [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Estimated insurance claim receivable				$ 177,400,000		$ 177,400,000
Proceeds from insurance claims on ViaSat-2 satellite		$ 2,300,000					185,700,000
Minimum [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Property, equipment and satellites, estimated useful life (years)					2 years
Estimated useful life, years					2 years
Minimum [Member] | Internally Developed Software [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Property, equipment and satellites, estimated useful life (years)					3 years
Minimum [Member] | CPE Leased Equipment [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Property, equipment and satellites, estimated useful life (years)					4 years
Minimum [Member] | Satellites [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Property, equipment and satellites, estimated useful life (years)					12 years
Maximum [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Property, equipment and satellites, estimated useful life (years)					17 years
Estimated useful life, years					10 years
Maximum [Member] | Software Development Costs [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Estimated useful life, years					5 years
Maximum [Member] | Internally Developed Software [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Property, equipment and satellites, estimated useful life (years)					7 years
Maximum [Member] | CPE Leased Equipment [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Property, equipment and satellites, estimated useful life (years)					5 years
Maximum [Member] | Satellites [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Property, equipment and satellites, estimated useful life (years)					17 years
Funded Research and Development from Customer Contracts [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Percentage of revenue	22.00%			17.00%	23.00%	17.00%
Operating Segments [Member] | Commercial Networks and Government Systems [Member] | Fixed-price Contract [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Percentage of revenue	89.00%			90.00%	88.00%	89.00%
U.S. Government as an Individual Customer [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Percentage of revenue	30.00%			29.00%	30.00%	29.00%
Commercial Customers [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Percentage of revenue	70.00%			71.00%	70.00%	71.00%
Unfavorable Regulatory Action [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Accrued reserves	$ 4,900,000				$ 4,900,000		4,900,000
Indemnification Agreement [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Accrued reserves	$ 0				$ 0		$ 0
Euro Retail Co [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Equity method investment ownership percentage			49.00%