Assets Purchased under Resale Agreements and Sold under Repurchase Agreements (Repurchase Agreements) (Details) - USD ($)	3 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Amount of securities sold under repurchase agreements
Gross repurchase agreements		$ 300,000,000	$ 450,000,000
Weighted average interest rates		3.25%	4.74%	4.46%
Repurchase agreements’ extinguishment cost	$ 8,700,000	$ 8,740,000	$ 0	$ 0
Extinguishment of repurchase agreements	$ 150,000,000.0