Investment Securities, Available-for-sale Securities, Gross Unrealized Loss Position (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Available for sale securities unrealized loss position - Fair Value [Abstract]
Less than 12 months - Fair Value	$ 150,864	$ 78,389
12 months or more - Fair Value	341,829	491,378
Total - Fair Value	492,693	569,767
Available for sale securities unrealized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	712	573
12 months or more - Gross Unrealized Loss	3,945	6,730
Total - Gross Unrealized Loss	4,657	7,303
U. S. government sponsored enterprises [Member]
Available for sale securities unrealized loss position - Fair Value [Abstract]
Less than 12 months - Fair Value	5,994	12,840
12 months or more - Fair Value	55,787	54,959
Total - Fair Value	61,781	67,799
Available for sale securities unrealized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	8	81
12 months or more - Gross Unrealized Loss	232	541
Total - Gross Unrealized Loss	240	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	136,827	65,549
12 months or more - Fair Value	184,915	325,476
Total - Fair Value	321,742	391,025
Available for sale securities unrealized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	608	492
12 months or more - Gross Unrealized Loss	1,648	3,163
Total - Gross Unrealized Loss	2,256	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	8,043	0
12 months or more - Fair Value	90,624	100,496
Total - Fair Value	98,667	100,496
Available for sale securities unrealized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	96	0
12 months or more - Gross Unrealized Loss	1,940	2,777
Total - Gross Unrealized Loss	2,036	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	10,503	10,447
Total - Fair Value	10,503	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	125	249
Total - Gross Unrealized Loss	$ 125	$ 249