Investment Securities, Available-for-sale Securities, Gross Unrealized Loss Position (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Available for sale securities unrealized loss position - Fair Value [Abstract]
Less than 12 months - Fair Value	$ 109,735	$ 77,814
12 months or more - Fair Value	436,666	481,405
Total - Fair Value	546,401	559,219
Available for sale securities unrealized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	2,135	637
12 months or more - Gross Unrealized Loss	13,850	8,224
Total - Gross Unrealized Loss	15,985	8,861
U. S. Government Sponsored Enterprises [Member]
Available for sale securities unrealized loss position - Fair Value [Abstract]
Less than 12 months - Fair Value	59,076	29,734
12 months or more - Fair Value	82,251	98,090
Total - Fair Value	141,327	127,824
Available for sale securities unrealized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	895	266
12 months or more - Gross Unrealized Loss	2,639	1,800
Total - Gross Unrealized Loss	3,534	2,066
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	45,441	48,080
12 months or more - Fair Value	250,721	266,394
Total - Fair Value	296,162	314,474
Available for sale securities unrealized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	1,221	371
12 months or more - Gross Unrealized Loss	8,900	4,344
Total - Gross Unrealized Loss	10,121	4,715
Corporate Bonds [Member]
Available for sale securities unrealized loss position - Fair Value [Abstract]
Less than 12 months - Fair Value	5,218	0
12 months or more - Fair Value	30,008	40,162
Total - Fair Value	35,227	40,162
Available for sale securities unrealized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	19	0
12 months or more - Gross Unrealized Loss	101	108
Total - Gross Unrealized Loss	120	108
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	64,113	67,059
Total - Fair Value	64,113	67,059
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	2,040	1,862
Total - Gross Unrealized Loss	2,040	1,862
Mortgage Backed Securities and Collateralized Mortgage Obligations-Commercial [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	9,573	9,700
Total - Fair Value	9,573	9,700
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	170	110
Total - Gross Unrealized Loss	$ 170	$ 110