Investment Securities, Available-for-sale Securities (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Amortized cost and fair value of the securities available for sale [Abstract]
Amortized Cost	$ 822,959	$ 893,821
Gross Unrealized Gains	2,039	467
Gross Unrealized Losses	13,228	30,534
Fair Value	811,770	863,754
U. S. government sponsored enterprises [Member]
Amortized cost and fair value of the securities available for sale [Abstract]
Amortized Cost	103,805	200,531
Gross Unrealized Gains	56	22
Gross Unrealized Losses	521	1,724
Fair Value	103,340	198,829
State and political subdivisions [Member]
Amortized cost and fair value of the securities available for sale [Abstract]
Amortized Cost	3,823	7,623
Gross Unrealized Gains	98	135
Gross Unrealized Losses	0	0
Fair Value	3,921	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	594,869	552,230
Gross Unrealized Gains	1,885	267
Gross Unrealized Losses	7,237	20,048
Fair Value	589,517	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	1	1
Fair Value	1,402	10,471
Small Business Administration-guaranteed participation securities [Member]
Amortized cost and fair value of the securities available for sale [Abstract]
Amortized Cost	107,542	111,383
Gross Unrealized Gains	0	0
Gross Unrealized Losses	5,175	8,354
Fair Value	102,367	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	10,832	10,965
Gross Unrealized Gains	0	0
Gross Unrealized Losses	288	407
Fair Value	10,544	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	822,924	893,811
Gross Unrealized Gains	2,039	467
Gross Unrealized Losses	13,228	30,534
Fair Value	811,735	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