Basis of Presentation - Additional Information (Detail)	1 Months Ended	3 Months Ended			6 Months Ended
	Jun. 30, 2025 USD ($)	Sep. 30, 2025 USD ($) shares	Jun. 30, 2025 USD ($)	Sep. 30, 2024 USD ($) shares	Sep. 30, 2025 USD ($) Segment shares	Sep. 30, 2024 USD ($) shares	Mar. 31, 2025 USD ($) shares	Mar. 31, 2024 USD ($)
Company And Summary Of Significant Accounting Policies [Line Items]
Revenue, practical expedient, financing component					true
Cash dividends	$ 155,700,000
Company's share of dividend					$ 96,000,000
Reduction to noncontrolling interest			$ 59,700,000		59,695,000
Distributions to minority shareholders		$ 13,800,000			59,695,000	$ 0
Remaining performance obligations		3,900,000,000			$ 3,900,000,000
Number of reportable segments | Segment					2
Decrease in collections in excess of revenues and deferred revenues					$ (5,700,000)
Collections in excess of revenues and deferred revenues, recognized revenue		71,700,000		$ 39,900,000	177,800,000	146,200,000
Capitalized interest expense		60,400,000		48,600,000	$ 115,600,000	105,200,000
Operating lease, existence of option to terminate					true
Operating lease, option to terminate, description					some of which include renewal options, and some of which include options to terminate the leases within one year.
Total capitalized costs related to patents		142,700,000			$ 142,700,000		$ 129,400,000
Accumulated amortization of patents, orbital slots and other licenses		16,900,000			16,900,000		10,200,000
Patents, orbital slots and other licenses amortization expense		3,500,000			6,800,000
Debt issuance costs capitalized					0	35,600,000
Self-insurance liability		5,500,000			5,500,000		5,900,000
Repurchase and immediate retirement of treasury shares pursuant to vesting of certain RSU agreements | value		1,956,000		980,000	6,624,000	2,395,000
Stock-based compensation expense					34,829,000	41,965,000
Continuing Operations [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Stock-based compensation expense		20,100,000		$ 22,800,000	$ 34,800,000	$ 42,000,000
Accounting Standards Update 2023-06 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements					In October 2023, the FASB issued ASU 2023-06, Disclosure Improvements: Codification Amendments in Response to the SEC’s Disclosure Update and Simplification Initiative. This ASU amends certain disclosure and presentation requirements for a variety of topics within the FASB ASC. These amendments will also align the requirements in the ASC with the SEC's regulations. The effective date for each amended topic in the ASC is the date on which the SEC’s removal of the related disclosure requirement from Regulation S-X or Regulation S-K becomes effective, and will not be effective if the SEC has not removed the applicable disclosure requirements by June 30, 2027. Early adoption is prohibited. The Company is currently evaluating the impact of this standard on its consolidated financial statements and disclosures.
Accounting Standards Update 2023-07 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements					In November 2023, the FASB issued ASU 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures. This ASU requires public entities to enhance disclosures about their reportable segments' significant expenses on an interim and annual basis. The Company adopted the new guidance for annual disclosures in fiscal year 2025 and for interim disclosures in the first quarter of fiscal year 2026 on a retrospective basis. See Note 10 — Segment Information for additional information.
Accounting Standards Update 2023-09 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements					In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures. ASU 2023-09 enhances annual income tax disclosures by requiring disclosure of specific categories in the income tax rate reconciliation table and disaggregation of income taxes paid. The new standard will become effective for the Company's annual disclosures beginning in fiscal year 2026. Early adoption is permitted and the new standard should be applied prospectively, however retrospective application is permitted. The Company is currently evaluating the impact of this standard on its consolidated financial statements and disclosures.
Accounting Standards Update 2024-02 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements					In March 2024, the FASB issued ASU 2024-02, Codification Improvements – Amendments to Remove References to the Concepts Statements. This update contains amendments to the Codification that remove references to various Concepts Statements. The amendments in this update are not intended to result in significant accounting changes for most entities. The Company adopted the new guidance on a prospective basis in the first quarter of fiscal year 2026 and the guidance did not have an impact on its consolidated financial statements and disclosures.
Accounting Standards Update 2024-03 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements					In November 2024, the FASB issued ASU 2024-03, Income Statement – Reporting Comprehensive Income – Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses. This ASU requires additional disclosures about certain categories of costs and expenses in the notes to financial statements. As clarified in ASU 2025-01, Income Statement – Reporting Comprehensive Income – Expense Disaggregation Disclosures (Subtopic 220-40): Clarifying the Effective Date, the new standard will become effective for the Company’s annual disclosures beginning in fiscal year 2028 and for interim disclosures beginning in fiscal year 2029. Early adoption is permitted and the amendments should be applied either prospectively to financial statements issued for reporting periods after the effective date of the ASU or retrospectively to any or all periods presented in the financial statements. The Company is currently evaluating the impact of this standard on its consolidated financial statements and disclosures.
Accounting Standards Update 2025-04 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements					In May 2025, the FASB issued ASU 2025-04, Compensation – Stock Compensation (Topic 718) and Revenue from Contracts with Customers (Topic 606): Clarifications to Share-Based Consideration Payable to a Customer. The purpose of this ASU is to reduce diversity in practice and improve the decision usefulness and operability of the guidance for share-based consideration payable to a customer in conjunction with selling goods or services. The new standard will become effective for the Company's interim and annual disclosures beginning in fiscal year 2028. Early adoption is permitted and the new guidance should be applied either on a modified retrospective or a retrospective basis. The Company is currently evaluating the impact of this standard on its consolidated financial statements and disclosures.
Accounting Standards Update 2025-05 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements					In July 2025, the FASB issued ASU 2025-05, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses for Accounts Receivable and Contract Assets. The purpose of this ASU is to allow entities to apply a practical expedient when estimating expected credit losses for current accounts receivable and current contract assets that arise from transactions accounted for under Topic 606. The new standard will become effective for the Company's interim and annual disclosures beginning in fiscal year 2027. Early adoption is permitted and the new guidance should be applied prospectively. The Company is currently evaluating the impact of this standard on its consolidated financial statements and disclosures.
Accounting Standards Update 2025-06 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements					In September 2025, FASB issued ASU 2025-06, Intangibles – Goodwill and Other – Internal-Use Software (Subtopic 350-40): Targeted Improvements to the Accounting for Internal-Use Software. The purpose of this ASU is to modernize the accounting guidance for the costs to develop software for internal use by removing all references to prescriptive and sequential software development project stages and providing further guidance on when an entity is required to start capitalizing eligible costs. The new standard will become effective for the Company's interim and annual disclosures beginning in fiscal year 2029. Early adoption is permitted and the new guidance should be applied either on prospective transition, modified transition or retrospective transition approach. The Company is currently evaluating the impact of this standard on its consolidated financial statements and disclosures.
Accounting Standards Update 2025-07 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements					In September 2025, FASB issued ASU 2025-07, Derivative and Hedging (Topic 815) and Revenue from Contracts with Customers (Topic 606): Derivatives Scope Refinements and Scope Clarification for Share-Based Noncash Consideration from a Customer in a Revenue Contract. This ASU expands the scope exception in Topic 815 and clarifies the guidance on share-based noncash consideration from a customer in Topic 606. The new standard will become effective for the Company's interim and annual disclosures beginning in fiscal year 2028. Early adoption is permitted and the new guidance should be applied either prospectively or on a modified retrospective basis. The Company is currently evaluating the impact of this standard on its consolidated financial statements and disclosures.
CPE Leased Equipment [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Property, equipment and satellites, cost		527,085,000			$ 527,085,000		525,972,000
Accumulated depreciation and amortization		343,600,000			343,600,000		328,000,000
Satellites [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Reduction to carrying value including capitalized interest								$ 1,670,000,000
Insurance claim receivables								$ 770,000,000
Unfavorable Regulatory Action [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Accrued reserves		15,100,000			15,100,000		14,800,000
Unfavorable Regulatory Action [Member] | Performance Obligations [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Accrued reserves		15,100,000			15,100,000		14,800,000
Indemnification Guarantee [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Accrued reserves		$ 0			$ 0		$ 0
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		226,081		150,045	1,578,052	370,158
Common Stock Held in Treasury [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Shares of common stock outstanding | shares		0			0		0
Repurchase and immediate retirement of treasury shares pursuant to vesting of certain RSU agreements, shares | shares		99,480		56,243	602,644	141,881
Repurchase and immediate retirement of treasury shares pursuant to vesting of certain RSU agreements | value		$ 2,000,000		$ 1,000,000	$ 6,600,000	$ 2,400,000