Assets Purchased under Resale Agreements and Sold under Repurchase Agreements (Resale Agreements and Repurchase Agreements) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Resale agreements
Gross resale agreements	$ 1,310,000		$ 1,160,000
Loans purchased under agreements to resell, increase	850,000		300,000
Repurchase agreements
Gross repurchase agreements	$ 300,000		$ 300,000
Weighted average interest rates	2.67%	4.10%
Securities Purchased Under Resale Agreements
Resale agreements
Weighted-average yields	1.57%	2.50%
Loans Purchased Under Resale Agreements
Resale agreements
Weighted-average yields	2.02%