Investment Securities, Available-for-sale Securities, Gross Unrealized Loss Position (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Available for sale securities unrealized loss position - Fair Value [Abstract]
Less than 12 months - Fair Value	$ 222,870	$ 78,389
12 months or more - Fair Value	343,024	491,378
Total - Fair Value	565,894	569,767
Available for sale securities unrealized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	2,522	573
12 months or more - Gross Unrealized Loss	6,721	6,730
Total - Gross Unrealized Loss	9,243	7,303
U. S. government sponsored enterprises [Member]
Available for sale securities unrealized loss position - Fair Value [Abstract]
Less than 12 months - Fair Value	31,493	12,840
12 months or more - Fair Value	56,351	54,959
Total - Fair Value	87,844	67,799
Available for sale securities unrealized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	51	81
12 months or more - Gross Unrealized Loss	170	541
Total - Gross Unrealized Loss	221	622
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	183,404	65,549
12 months or more - Fair Value	188,924	325,476
Total - Fair Value	372,328	391,025
Available for sale securities unrealized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	2,307	492
12 months or more - Gross Unrealized Loss	3,818	3,163
Total - Gross Unrealized Loss	6,125	3,655
Small Business Administration-guaranteed participation securities [Member]
Available for sale securities unrealized loss position - Fair Value [Abstract]
Less than 12 months - Fair Value	7,973	0
12 months or more - Fair Value	87,350	100,496
Total - Fair Value	95,323	100,496
Available for sale securities unrealized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	164	0
12 months or more - Gross Unrealized Loss	2,572	2,777
Total - Gross Unrealized Loss	2,736	2,777
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	10,399	10,447
Total - Fair Value	10,399	10,447
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	161	249
Total - Gross Unrealized Loss	$ 161	$ 249