Investment Securities, Available-for-sale Securities, Gross Unrealized Loss Position (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Available for sale securities unrealized loss position - Fair Value [Abstract]
Less than 12 months - Fair Value	$ 32,467	$ 45,915
12 months or more - Fair Value	428,797	438,490
Total - Fair Value	461,264	484,405
Available for sale securities unrealized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	345	215
12 months or more - Gross Unrealized Loss	9,452	13,911
Total - Gross Unrealized Loss	9,797	14,126
U. S. Government Sponsored Enterprises [Member]
Available for sale securities unrealized loss position - Fair Value [Abstract]
Less than 12 months - Fair Value	0	29,870
12 months or more - Fair Value	123,289	112,291
Total - Fair Value	123,289	142,161
Available for sale securities unrealized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	0	106
12 months or more - Gross Unrealized Loss	1,604	2,602
Total - Gross Unrealized Loss	1,604	2,708
Mortgage-Backed Securities and Collateralized Mortgage Obligations - Residential [Member]
Available for sale securities unrealized loss position - Fair Value [Abstract]
Less than 12 months - Fair Value	27,597	1,102
12 months or more - Fair Value	251,395	259,729
Total - Fair Value	278,992	260,831
Available for sale securities unrealized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	215	11
12 months or more - Gross Unrealized Loss	5,901	9,396
Total - Gross Unrealized Loss	6,116	9,407
Corporate Bonds [Member]
Available for sale securities unrealized loss position - Fair Value [Abstract]
Less than 12 months - Fair Value	4,870	14,943
12 months or more - Fair Value	0	9,995
Total - Fair Value	4,870	24,938
Available for sale securities unrealized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	130	98
12 months or more - Gross Unrealized Loss	0	12
Total - Gross Unrealized Loss	130	110
Small Business Administration-Guaranteed Participation Securities [Member]
Available for sale securities unrealized loss position - Fair Value [Abstract]
Less than 12 months - Fair Value	0	0
12 months or more - Fair Value	54,113	56,475
Total - Fair Value	54,113	56,475
Available for sale securities unrealized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	0	0
12 months or more - Gross Unrealized Loss	1,947	1,901
Total - Gross Unrealized Loss	$ 1,947	$ 1,901