Securities (Details) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Securities available-for-sale: [Abstract]
Amortized Cost	$ 675,927,000	$ 857,555,000
Gross Unrealized Gains	31,827,000	37,809,000
Gross Unrealized Losses	1,176,000	402,000
Fair Value	706,578,000	894,962,000
Securities held-to-maturity: [Abstract]
Amortized Cost	575,000	2,330,000
Gross Unrealized Gains	8,000	39,000
Gross Unrealized Losses	0	0
Fair Value	583,000	2,369,000
Securities pledged as collateral to secure public funds and other deposits or securities sold under agreements to repurchase	612,100,000
Available-for-sale, Amortized Cost [Abstract]
Due in one year or less	4,480,000
Due in one year to five years	34,791,000
Due in five years to ten years	125,863,000
Due after ten years	132,928,000
Mortgage-backed securities	360,504,000
Asset-backed securities	17,361,000
Amortized Cost	675,927,000
Available-for-sale, Fair Value [Abstract]
Due in one year or less	4,524,000
Due in one year to five years	36,140,000
Due in five years to ten years	133,944,000
Due after ten years	138,967,000
Mortgage-backed securities	375,651,000
Asset-backed securities	17,352,000
Fair Value	706,578,000
Held-to-maturity, Amortized Cost [Abstract]
Due in one year or less	200,000
Due in one year to five years	375,000
Due in five years to ten years	0
Due after ten years	0
Mortgage-backed securities	0
Asset-backed securities	0
Amortized Cost	575,000
Held-to-maturity, Fair Value [Abstract]
Due in one year or less	201,000
Due in one year to five years	382,000
Due in five years to ten years	0
Due after ten years	0
Mortgage-backed securities	0
Asset-backed securities	0
Fair Value	583,000
U.S. Government Agency Securities [Member]
Securities available-for-sale: [Abstract]
Amortized Cost	110,817,000	41,978,000
Gross Unrealized Gains	49,000	344,000
Gross Unrealized Losses	414,000	9,000
Fair Value	110,452,000	42,313,000
Mortgage-backed Securities [Member]
Securities available-for-sale: [Abstract]
Amortized Cost	360,504,000	623,684,000
Gross Unrealized Gains	15,770,000	22,254,000
Gross Unrealized Losses	623,000	371,000
Fair Value	375,651,000	645,567,000
State and Municipal Securities [Member]
Securities available-for-sale: [Abstract]
Amortized Cost	177,364,000	182,206,000
Gross Unrealized Gains	14,489,000	13,768,000
Gross Unrealized Losses	126,000	22,000
Fair Value	191,727,000	195,952,000
Securities held-to-maturity: [Abstract]
Amortized Cost	575,000	2,330,000
Gross Unrealized Gains	8,000	39,000
Gross Unrealized Losses	0	0
Fair Value	583,000	2,369,000
Asset-backed Securities [Member]
Securities available-for-sale: [Abstract]
Amortized Cost	17,361,000
Gross Unrealized Gains	0
Gross Unrealized Losses	9,000
Fair Value	17,352,000
Corporate Notes [Member]
Securities available-for-sale: [Abstract]
Amortized Cost	9,881,000	9,687,000
Gross Unrealized Gains	1,519,000	1,443,000
Gross Unrealized Losses	4,000	0
Fair Value	$ 11,396,000	$ 11,130,000