Assets Purchased under Resale Agreements and Sold under Repurchase Agreements (Resale Agreements and Repurchase Agreements) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Resale agreements
Gross resale agreements	$ 1,340,000		$ 1,340,000		$ 1,160,000
Loans purchased under agreements to resell, increase	1,260,000		1,260,000		300,000
Repurchase agreements
Gross repurchase agreements	$ 300,000		$ 300,000		$ 300,000
Weighted average interest rates	2.57%	2.70%	2.62%	3.64%
Securities Purchased Under Resale Agreements
Resale agreements
Weighted-average yields	1.50%	1.72%	1.53%	2.09%
Loans Purchased Under Resale Agreements
Resale agreements
Weighted-average yields	1.48%		1.57%