Debt - Debentures (Parenthetical) (Details) - Unsecured debt	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
7.950% Debentures due 2025
Debt Instrument [Line Items]
Interest rate	7.95%	7.95%
Debt instrument maturity year	2025	2025
8.375% Debentures due 2027
Debt Instrument [Line Items]
Interest rate	8.375%	8.375%
Debt instrument maturity year	2027	2027