Investment Securities, Available-for-sale Securities (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Amortized cost and fair value of the securities available for sale [Abstract]
Amortized Cost	$ 735,457	$ 893,821
Gross Unrealized Gains	809	467
Gross Unrealized Losses	13,643	30,534
Fair Value	722,623	863,754
U. S. government sponsored enterprises [Member]
Amortized cost and fair value of the securities available for sale [Abstract]
Amortized Cost	83,805	200,531
Gross Unrealized Gains	17	22
Gross Unrealized Losses	735	1,724
Fair Value	83,087	198,829
State and political subdivisions [Member]
Amortized cost and fair value of the securities available for sale [Abstract]
Amortized Cost	2,681	7,623
Gross Unrealized Gains	88	135
Gross Unrealized Losses	0	0
Fair Value	2,769	7,758
Mortgage-backed securities and collateralized mortgage obligations-residential [Member]
Amortized cost and fair value of the securities available for sale [Abstract]
Amortized Cost	530,688	552,230
Gross Unrealized Gains	704	267
Gross Unrealized Losses	7,613	20,048
Fair Value	523,779	532,449
Corporate bonds [Member]
Amortized cost and fair value of the securities available for sale [Abstract]
Amortized Cost	1,403	10,429
Gross Unrealized Gains	0	43
Gross Unrealized Losses	2	1
Fair Value	1,401	10,471
Small Business Administration-guaranteed participation securities [Member]
Amortized cost and fair value of the securities available for sale [Abstract]
Amortized Cost	105,430	111,383
Gross Unrealized Gains	0	0
Gross Unrealized Losses	4,939	8,354
Fair Value	100,491	103,029
Mortgage-backed securities and collateralized mortgage obligations-Commercial [Member]
Amortized cost and fair value of the securities available for sale [Abstract]
Amortized Cost	10,765	10,965
Gross Unrealized Gains	0	0
Gross Unrealized Losses	348	407
Fair Value	10,417	10,558
Other [Member]
Amortized cost and fair value of the securities available for sale [Abstract]
Amortized Cost	650	650
Gross Unrealized Gains	0	0
Gross Unrealized Losses	6	0
Fair Value	644	650
Debt securities [Member]
Amortized cost and fair value of the securities available for sale [Abstract]
Amortized Cost	735,422	893,811
Gross Unrealized Gains	809	467
Gross Unrealized Losses	13,643	30,534
Fair Value	722,588	863,744
Equity securities [Member]
Amortized cost and fair value of the securities available for sale [Abstract]
Amortized Cost	35	10
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	$ 35	$ 10