Fair Value Measurements - Additional Information (Detail) € in Millions		3 Months Ended	12 Months Ended
	Apr. 30, 2021 USD ($)	Sep. 30, 2023 USD ($)	Mar. 31, 2026 USD ($)	Mar. 31, 2025 USD ($)	Sep. 30, 2024	Sep. 28, 2023	Apr. 30, 2021 EUR (€)
Satellite Performance Incentives Obligation [Member] | Satellites [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]
Interest rate on the outstanding borrowings			5.625%
2027 Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate on the outstanding borrowings			5.625%
2028 Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate on the outstanding borrowings			6.50%
2031 Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate on the outstanding borrowings						7.50%
Ex-Im Credit Facility [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate on the outstanding borrowings			4.78%
Inmarsat Senior Secured Notes due 2026 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate on the outstanding borrowings			6.75%
Inmarsat Senior Secured Notes 2029 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate on the outstanding borrowings					9.00%
Euro Broadband Infrastructure Sarl 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 received €20.0 million, or approximately $22.0 million, in cash and recorded a gain of approximately $18.1 million in the second quarter of fiscal year 2024 in selling, general and administrative expenses in the consolidated statements of operations and comprehensive income (loss).
Euro Broadband Infrastructure Sarl 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	$ 22,000,000						€ 20.0
Contingency gain recognized in current period		$ 18,100,000
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 2 [Member] | Satellite Performance Incentives Obligation [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Satellite performance incentives obligation			6,100,000	11,400,000
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				$ 438,600,000
Interest rate on the outstanding borrowings				5.625%
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			597,800,000	$ 575,000,000
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			395,000,000	350,000,000
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | 2031 Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of long term debt			724,900,000	552,800,000
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			186,200,000	19,200,000
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Inmarsat Senior Secured Notes 2029 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of long term debt			$ 2,070,000,000.00	$ 1,820,000,000