Securities (Schedule of Book Values and Fair Values of Investment Securities by Contractual Maturity) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Amortized Cost
Due within one year	$ 0
Due after one year but within five years	28,680
Due after five years but within ten years	79,016
Due after ten years	11,000
Mortgage-backed securities	1,024,735
Amortized Cost	1,143,431	$ 812,202
Fair Value
Due within one year	0
Due after one year but within five years	30,423
Due after five years but within ten years	79,560
Due after ten years	10,801
Mortgage-backed securities	1,047,922
Total securities	1,168,706	821,945
Amortized Cost
Due within one year	1,496
Due after one year but within five years	3,957
Due after five years but within ten years	5,877
Due after ten years	65,648
Mortgage-backed securities	33,222
Amortized Cost	110,200	67,932
Fair Value
Due within one year	1,509
Due after one year but within five years	4,075
Due after five years but within ten years	5,985
Due after ten years	66,384
Mortgage-backed securities	34,161
Total securities	$ 112,114	$ 68,333