Securities (Schedule of Book Values and Fair Values of Investment Securities by Contractual Maturity) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Amortized Cost
Due within one year	$ 0
Due after one year but within five years	58,721
Due after five years but within ten years	0
Due after ten years	5,000
Mortgage-backed securities	634,176
Amortized Cost	697,897	$ 513,741
Fair Value
Due within one year	0
Due after one year but within five years	59,661
Due after five years but within ten years	0
Due after ten years	5,075
Mortgage-backed securities	640,488
Total securities	705,224	501,351
Amortized Cost
Due within one year	1,165
Due after one year but within five years	21,645
Due after five years but within ten years	6,673
Due after ten years	814
Mortgage-backed securities	43,968
Amortized Cost	74,265	101,237
Fair Value
Due within one year	1,168
Due after one year but within five years	21,925
Due after five years but within ten years	6,718
Due after ten years	853
Mortgage-backed securities	43,801
Total securities	$ 74,465	$ 99,906