Securities (Schedule of Book Values and Fair Values of Investment Securities by Contractual Maturity) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Amortized Cost
Due within one year	$ 0
Due after one year but within five years	77,691
Due after five years but within ten years	10,242
Due after ten years	5,000
Mortgage-backed securities	593,824
Amortized Cost	686,757	$ 513,741
Fair Value
Due within one year	0
Due after one year but within five years	78,421
Due after five years but within ten years	10,473
Due after ten years	5,053
Mortgage-backed securities	598,024
Total securities	691,971	501,351	$ 334,068
Amortized Cost
Due within one year	1,165
Due after one year but within five years	22,463
Due after five years but within ten years	8,110
Due after ten years	865
Mortgage-backed securities	46,447
Amortized Cost	79,050	101,237	108,265
Fair Value
Due within one year	1,169
Due after one year but within five years	22,813
Due after five years but within ten years	8,165
Due after ten years	899
Mortgage-backed securities	45,998
Total securities	$ 79,044	$ 99,906	$ 107,068