Securities (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2014 item	Mar. 31, 2013	Dec. 31, 2013
Available for sale
Amortized Cost	$ 844,447,000		$ 833,735,000
Gross Unrealized Gains	11,078,000		11,350,000
Gross Unrealized Losses	(2,689,000)		(3,775,000)
Fair Value	852,836,000		841,310,000
Held to maturity
Amortized Cost	1,857,000		834,000
Gross Unrealized Gains	5,000		1,000
Gross Unrealized Losses	(3,000)		(4,000)
Fair Value	1,859,000		831,000
Available for sale, Amortized Cost
Due in one year or less	130,245,000
Due after one year through five years	374,490,000
Due after five years through ten years	165,832,000
Due after ten years	170,523,000
Amortized Cost	841,090,000
Available for sale, Fair Value
Due in one year or less	131,111,000
Due after one year through five years	377,005,000
Due after five years through ten years	168,511,000
Due after ten years	171,220,000
Fair Value	847,847,000
Held to maturity, Amortized Cost
Due after one year through five years	319,000
Due after five years through ten years	1,538,000
Amortized Cost	1,857,000		834,000
Held to maturity, Fair Value
Due after one year through five years	320,000
Due after five years through ten years	1,539,000
Fair Value	1,859,000		831,000
Realized gains and losses related to sales of securities available for sale
Gross security gains	57,000
Gross security (losses)	(14,000)
Net security gains	43,000
Tax provision related to net realized gains (losses)		0
Carrying amount of investment securities pledged as collateral	362,400,000		428,700,000
Available for sale, Fair Value
Continuous unrealized losses existing for less than 12 months, gross	230,024,000		199,636,000
Continuous unrealized losses existing greater than 12 months, gross	5,332,000		8,492,000
Total	235,356,000		208,128,000
Available for sale, Unrealized Losses
Continuous unrealized losses existing for less than 12 months, gross	2,474,000		3,481,000
Continuous unrealized losses existing greater than 12 months, gross	215,000		294,000
Total	2,689,000		3,775,000
Held to maturity, Fair Value
Continuous unrealized losses existing for less than 12 months, gross	1,303,000		597,000
Total	1,303,000		597,000
Held to maturity, Unrealized Losses
Continuous unrealized losses existing for less than 12 months, gross	3,000		4,000
Total	3,000		4,000
Number of securities in unrealized loss position	212
Securities in unrealized loss position as a percentage of aggregate carrying value of investments	1.10%
Debt securities
Available for sale
Amortized Cost	841,090,000		829,621,000
Gross Unrealized Gains	9,446,000		9,598,000
Gross Unrealized Losses	(2,689,000)		(3,775,000)
Fair Value	847,847,000		835,444,000
U.S. Treasury securities
Available for sale
Amortized Cost	50,464,000		102,463,000
Gross Unrealized Gains	217,000		244,000
Gross Unrealized Losses	(11,000)		(67,000)
Fair Value	50,670,000		102,640,000
Available for sale, Fair Value
Continuous unrealized losses existing for less than 12 months, gross	851,000		25,830,000
Total	851,000		25,830,000
Available for sale, Unrealized Losses
Continuous unrealized losses existing for less than 12 months, gross	11,000		67,000
Total	11,000		67,000
Obligations of U.S. government corporations and agencies
Available for sale
Amortized Cost	229,335,000		254,998,000
Gross Unrealized Gains	2,201,000		2,741,000
Gross Unrealized Losses	(291,000)		(328,000)
Fair Value	231,245,000		257,411,000
Available for sale, Fair Value
Continuous unrealized losses existing for less than 12 months, gross	25,992,000		25,946,000
Total	25,992,000		25,946,000
Available for sale, Unrealized Losses
Continuous unrealized losses existing for less than 12 months, gross	291,000		328,000
Total	291,000		328,000
Obligations of states and political subdivisions
Available for sale
Amortized Cost	252,019,000		272,077,000
Gross Unrealized Gains	3,177,000		2,887,000
Gross Unrealized Losses	(1,474,000)		(2,812,000)
Fair Value	253,722,000		272,152,000
Held to maturity
Amortized Cost	831,000		834,000
Gross Unrealized Gains	5,000		1,000
Gross Unrealized Losses			(4,000)
Fair Value	836,000		831,000
Held to maturity, Amortized Cost
Amortized Cost	831,000		834,000
Held to maturity, Fair Value
Fair Value	836,000		831,000
Available for sale, Fair Value
Continuous unrealized losses existing for less than 12 months, gross	73,682,000		92,703,000
Continuous unrealized losses existing greater than 12 months, gross	5,332,000		8,492,000
Total	79,014,000		101,195,000
Available for sale, Unrealized Losses
Continuous unrealized losses existing for less than 12 months, gross	1,259,000		2,518,000
Continuous unrealized losses existing greater than 12 months, gross	215,000		294,000
Total	1,474,000		2,812,000
Held to maturity, Fair Value
Continuous unrealized losses existing for less than 12 months, gross	280,000		597,000
Total	280,000		597,000
Held to maturity, Unrealized Losses
Continuous unrealized losses existing for less than 12 months, gross			4,000
Total			4,000
Obligations of states and political subdivisions | Maximum
Held to maturity, Unrealized Losses
Total			1,000
Residential mortgage-backed securities
Available for sale
Amortized Cost	266,556,000		174,699,000
Gross Unrealized Gains	3,694,000		3,571,000
Gross Unrealized Losses	(796,000)		(535,000)
Fair Value	269,454,000		177,735,000
Available for sale, Fair Value
Continuous unrealized losses existing for less than 12 months, gross	111,493,000		53,543,000
Total	111,493,000		53,543,000
Available for sale, Unrealized Losses
Continuous unrealized losses existing for less than 12 months, gross	796,000		535,000
Total	796,000		535,000
Corporate debt securities
Available for sale
Amortized Cost	42,716,000		25,384,000
Gross Unrealized Gains	157,000		155,000
Gross Unrealized Losses	(117,000)		(33,000)
Fair Value	42,756,000		25,506,000
Available for sale, Fair Value
Continuous unrealized losses existing for less than 12 months, gross	18,006,000		1,614,000
Total	18,006,000		1,614,000
Available for sale, Unrealized Losses
Continuous unrealized losses existing for less than 12 months, gross	117,000		33,000
Total	117,000		33,000
Mutual funds and other equity securities
Available for sale
Amortized Cost	3,357,000		4,114,000
Gross Unrealized Gains	1,632,000		1,752,000
Fair Value	4,989,000		5,866,000
Commercial mortgage-backed securities
Held to maturity
Amortized Cost	1,026,000
Gross Unrealized Losses	(3,000)
Fair Value	1,023,000
Held to maturity, Amortized Cost
Amortized Cost	1,026,000
Held to maturity, Fair Value
Fair Value	1,023,000
Held to maturity, Fair Value
Continuous unrealized losses existing for less than 12 months, gross	1,023,000
Total	1,023,000
Held to maturity, Unrealized Losses
Continuous unrealized losses existing for less than 12 months, gross	3,000
Total	$ 3,000