Securities (Schedule of Information Regarding Securities with Unrealized Losses) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Total temporarily impaired securities Fair Value	$ 272,454	$ 214,027
Total temporarily impaired securities Unrealized Losses	7,350	1,782
Total temporarily impaired securities Fair Value	121,374	128,965
Total temporarily impaired securities Unrealized Losses	4,177	1,972
Total temporarily impaired securities Fair Value	393,828	342,992
Total temporarily impaired securities Unrealized Losses	11,527	3,754
Government-sponsored enterprise securities [Member]
AFS Fair Value	15,673	10,897
AFS Unrealized Losses	326	103
AFS Fair Value	2,930	2,970
AFS Unrealized Losses	70	30
Total temporarily impaired securities Fair Value	18,603	13,867
Total temporarily impaired securities Unrealized Losses	396	133
Mortgage-backed securities [Member]
AFS Fair Value	222,384	192,702
AFS Unrealized Losses	6,583	1,582
AFS Fair Value	117,509	125,060
AFS Unrealized Losses	4,042	1,877
Total temporarily impaired securities Fair Value	339,893	317,762
Total temporarily impaired securities Unrealized Losses	10,625	3,459
Corporate bonds [Member]
AFS Fair Value	24,852	2,500
AFS Unrealized Losses	376	49
AFS Fair Value	935	935
AFS Unrealized Losses	65	65
Total temporarily impaired securities Fair Value	25,787	3,435
Total temporarily impaired securities Unrealized Losses	441	114
State and local governments [Member]
HTM Fair Value	9,545	7,928
HTM Unrealized Losses	65	48
AFS Fair Value
AFS Unrealized Losses
Total temporarily impaired securities Fair Value	9,545	7,928
Total temporarily impaired securities Unrealized Losses	$ 65	$ 48