Senior Notes and Other Long-Term Debt - Components of Long-Term Debt (Detail) - USD ($) $ in Thousands		Sep. 30, 2025	Mar. 31, 2025
Debt Instrument [Line Items]
Finance lease obligations (see Note 1)		$ 150,701	$ 158,473
Finance Lease, Liability, Statement of Financial Position [Extensible Enumeration]		Other long-term debt	Other long-term debt
Total debt		$ 6,731,043	$ 7,204,275
Unamortized discount, debt issuance costs and fair value adjustments made in purchase accounting		(146,808)	(168,166)
Less: current portion of long-term debt		49,503	503,825
Total long-term debt		6,534,732	6,532,284
2024 Inmarsat Term Loan Facility [Member]
Debt Instrument [Line Items]
Principal amount of debt		1,280,500	1,287,000
2022 Term Loan Facility [Member]
Debt Instrument [Line Items]
Principal amount of debt		677,250	680,750
2023 Term Loan Facility [Member]
Debt Instrument [Line Items]
Principal amount of debt		604,366	607,450
Immarsat Original Term Loan Facility [ Member]
Debt Instrument [Line Items]
Principal amount of debt		300,000	300,000
Ex-Im Credit Facility [Member]
Debt Instrument [Line Items]
Principal amount of debt	[1]	9,826	19,652
2025 Notes [Member]
Debt Instrument [Line Items]
Principal amount of debt	[2]		442,550
2027 Notes [Member]
Debt Instrument [Line Items]
Principal amount of debt		600,000	600,000
2028 Notes [Member]
Debt Instrument [Line Items]
Principal amount of debt		400,000	400,000
Inmarsat 2029 Notes [Member]
Debt Instrument [Line Items]
Principal amount of debt		1,975,000	1,975,000
2031 Notes [Member]
Debt Instrument [Line Items]
Principal amount of debt		$ 733,400	$ 733,400

[1] Subsequent to the second quarter of fiscal year 2026, the Ex-Im Credit Facility was fully repaid at maturity on October 15, 2025.

[2] On May 2, 2025, the 2025 Notes were redeemed in full.