Securities (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Securities available-for-sale: [Abstract]
Amortized Cost	$ 659,947,000		$ 675,927,000
Gross Unrealized Gains	26,837,000		31,827,000
Gross Unrealized Losses	3,239,000		1,176,000
Fair Value	683,545,000		706,578,000
Securities held-to-maturity: [Abstract]
Amortized Cost	40,459,000		575,000
Gross Unrealized Gains	9,000		8,000
Gross Unrealized Losses	91,000		0
Fair Value	40,377,000		583,000
Securities pledged as collateral to secure public funds and other deposits or securities sold under agreements to repurchase	612,300,000
Available for sale securities, transfers	39,959,647	0
Available-for-sale, Amortized Cost [Abstract]
Due in one year or less	9,570,000
Due in one year to five years	20,923,000
Due in five years to ten years	142,376,000
Due after ten years	110,983,000
Mortgage-backed securities	358,702,000
Asset-backed securities	17,393,000
Amortized Cost	659,947,000
Available-for-sale, Fair Value [Abstract]
Due in one year or less	9,717,000
Due in one year to five years	21,543,000
Due in five years to ten years	149,503,000
Due after ten years	113,567,000
Mortgage-backed securities	371,857,000
Asset-backed securities	17,358,000
Fair Value	683,545,000
Held-to-maturity, Amortized Cost [Abstract]
Due in one year or less	1,891,000
Due in one year to five years	1,016,000
Due in five years to ten years	9,510,000
Due after ten years	28,042,000
Mortgage-backed securities	0
Asset-backed securities	0
Amortized Cost	40,459,000
Held-to-maturity, Fair Value [Abstract]
Due in one year or less	1,891,000
Due in one year to five years	1,021,000
Due in five years to ten years	9,509,000
Due after ten years	27,956,000
Mortgage-backed securities	0
Asset-backed securities	0
Fair Value	40,377,000
U.S. Government Agency Securities [Member]
Securities available-for-sale: [Abstract]
Amortized Cost	139,609,000		110,817,000
Gross Unrealized Gains	55,000		49,000
Gross Unrealized Losses	1,420,000		414,000
Fair Value	138,244,000		110,452,000
Mortgage-backed Securities [Member]
Securities available-for-sale: [Abstract]
Amortized Cost	358,702,000		360,504,000
Gross Unrealized Gains	14,750,000		15,770,000
Gross Unrealized Losses	1,595,000		623,000
Fair Value	371,857,000		375,651,000
State and Municipal Securities [Member]
Securities available-for-sale: [Abstract]
Amortized Cost	134,731,000		177,364,000
Gross Unrealized Gains	10,563,000		14,489,000
Gross Unrealized Losses	187,000		126,000
Fair Value	145,107,000		191,727,000
Asset-backed Securities [Member]
Securities available-for-sale: [Abstract]
Amortized Cost	17,393,000		17,361,000
Gross Unrealized Gains	0		0
Gross Unrealized Losses	35,000		9,000
Fair Value	17,358,000		17,352,000
Corporate Notes and other [Member]
Securities available-for-sale: [Abstract]
Amortized Cost	9,512,000		9,881,000
Gross Unrealized Gains	1,469,000		1,519,000
Gross Unrealized Losses	2,000		4,000
Fair Value	$ 10,979,000		$ 11,396,000