Securities Purchased under Resale Agreements and Sold under Repurchase Agreements (Resale Agreements and Repurchase Agreements) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Resale agreements
Gross resale agreements	$ 1,260,000		$ 1,260,000		$ 1,110,000
Weighted-average yields	2.14%	2.71%	2.32%	2.77%
Repurchase agreements
Gross repurchase agreements	$ 300,000		$ 300,000		$ 450,000
Weighted-average rates	3.40%	4.93%	3.76%	4.97%
Repurchase agreements’ extinguishment costs	$ 8,740	$ 0	$ 8,740	$ 0
Extinguishment of repurchase agreements	150,000		150,000
Maturity, 2023	$ 300,000		$ 300,000