Financing Agreements - Borrowings Under Repurchase Agreement (Details) - Repurchase Agreement Borrowings - Fair Value - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	$ 3,943,493	$ 3,501,876
Weighted Average Interest Rate	2.59%	2.38%
Within 30 days
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	$ 3,629,100	$ 3,222,268
Weighted Average Interest Rate	2.57%	2.36%
Over 30 days to 3 months
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	$ 268,202	$ 257,444
Weighted Average Interest Rate	2.46%	2.49%
Over 3 months to 12 months
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	$ 46,191	$ 22,164
Weighted Average Interest Rate	4.36%	4.50%
Over 12 months
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	$ 0	$ 0
Weighted Average Interest Rate	0.00%	0.00%