Securities (Schedule of Book Values and Fair Values of Investment Securities by Contractual Maturity) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Amortized Cost
Due within one year	$ 0
Due after one year but within five years	28,701
Due after five years but within ten years	15,000
Due after ten years	5,000
Mortgage-backed securities	727,261
Amortized Cost	775,962	$ 812,202
Fair Value
Due within one year	0
Due after one year but within five years	29,567
Due after five years but within ten years	15,032
Due after ten years	4,945
Mortgage-backed securities	756,926
Total securities	806,470	821,945
Amortized Cost
Due within one year	1,730
Due after one year but within five years	11,496
Due after five years but within ten years	5,342
Due after ten years	3,622
Mortgage-backed securities	39,113
Amortized Cost	61,303	67,932
Fair Value
Due within one year	1,750
Due after one year but within five years	11,639
Due after five years but within ten years	5,389
Due after ten years	3,615
Mortgage-backed securities	39,992
Total securities	$ 62,385	$ 68,333