Securities Purchased under Resale Agreements and Sold under Repurchase Agreements (Resale Agreements and Repurchase Agreements) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Resale agreements
Gross resale agreements	$ 860,000		$ 1,110,000
Weighted-average yields	2.54%	2.80%
Repurchase agreements
Gross repurchase agreements	$ 450,000		$ 450,000
Weighted-average rates	4.10%	5.01%
Maturity, 2022	$ 150,000
Maturity, 2023	$ 300,000