Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended
	Jun. 30, 2025	Mar. 31, 2025	Sep. 30, 2024	Sep. 28, 2023
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	2.38%
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%
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	10,400,000	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	597,500,000	$ 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	378,000,000	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	635,400,000	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	9,700,000	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	$ 1,990,000,000	$ 1,820,000,000