Securities (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 1,213,934,000	$ 1,111,290,000
Unrealized gains	30,839,000	24,986,000
Unrealized losses	154,000	6,908,000
Estimated fair value	1,244,619,000	1,129,368,000
Amortized Cost of mortgage-backed securities comprised of Government Sponsored Enterprise Securities	290,200,000	208,900,000
Fair value of mortgage-backed securities comprised of Government Sponsored Enterprise Securities	303,000,000	217,900,000
Amortized Cost of mortgage-backed securities comprised of US Government Agency Securities	20,500,000	25,000,000
Fair value of mortgage-backed securities comprised of US Government Agency Securities	22,400,000	26,900,000
Amortized Cost of Collateralized Mortgage Obligations comprised of Government Sponsored Enterprise Securities	398,300,000	206,000,000
Fair Value of Collateralized Mortgage Obligations comprised of Government Sponsored Enterprise Securities	402,400,000	207,000,000
Amortized Cost of Collateralized Mortgage Obligations comprised of US Government Agency Securities	60,800,000	87,600,000
Fair Value of Collateralized Mortgage Obligations comprised of US Government Agency Securities	63,100,000	90,800,000
Investment securities with unrealized losses [Abstract]
Unrealized Loss Position, Less Than 12 Months, Fair Value	63,966,000	327,056,000
Unrealized Loss Position, Less Than 12 Months, Unrealized Losses	(153,000)	(6,570,000)
Unrealized Loss Position, Less Than 12 Months, Number of Positions	11	54
Unrealized Loss Position, 12 Months or Longer, Fair Value	377,000	7,533,000
Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	(1,000)	(338,000)
Unrealized Loss Position, 12 Months or Longer, Number of Positions	2	19
Unrealized Loss Position, Total, Fair Value	64,343,000	334,589,000
Unrealized Loss Position, Total, Unrealized Losses	(154,000)	(6,908,000)
Unrealized Loss Position, Total, Number of Positions	13	73
Consolidated stockholders' equity threshold percentage that no single issuer of securities exceeded except for U.S. Government securities. (in hundredths)	10.00%	10.00%
Sales transactions of securities available for sale [Abstract]
Proceeds from sales	2,437,000	103,253,000	2,753,000
Gross realized gains	7,000	3,170,000	154,000
Gross realized losses	(165,000)	(25,000)	(49,000)
Net securities (losses) gains excluding gains from calls	(158,000)	3,145,000	105,000
Gains from calls on securities available for sale	300,000	100,000
Amortized costs of securities available for sale pledged to secure public deposits	1,200,000,000	900,000,000
Amortized costs of securities available for sale pledged as collateral for repurchase agreements	141,700,000
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	70,811,000	97,310,000
Unrealized gains	1,387,000	1,449,000
Unrealized losses	0	0
Estimated fair value	72,198,000	98,759,000
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis [Abstract]
Within one year	23,867,000
From one to five years	302,772,000
From five to ten years	245,058,000
After ten years	633,302,000
Total, Amortized Cost	1,204,999,000
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Within one year	23,941,000
From one to five years	305,366,000
From five to ten years	254,864,000
After ten years	649,568,000
Total, Fair Value	1,233,739,000
Debt Securities Classified as Held to Maturity [Abstract]
Within one year	26,315,000
From one to five years	34,032,000
From five to ten years	7,073,000
After ten years	3,391,000
Securities held to maturity	70,811,000	97,310,000
Held-to-maturity Securities, Debt Maturities, Fair Value [Abstract]
Within one year	26,383,000
From one to five years	35,058,000
From five to ten years	7,153,000
After ten years	3,604,000
Total, Fair Value	72,198,000
State & municipal [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	69,364,000	95,591,000
Unrealized gains	1,174,000	1,249,000
Unrealized losses	0	0
Estimated fair value	70,538,000	96,840,000
Debt Securities Classified as Held to Maturity [Abstract]
Securities held to maturity	69,364,000	95,591,000
Mortgage-backed [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	1,447,000	1,719,000
Unrealized gains	213,000	200,000
Unrealized losses	0	0
Estimated fair value	1,660,000	1,919,000
Debt Securities Classified as Held to Maturity [Abstract]
Securities held to maturity	1,447,000	1,719,000
US Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	81,006,000	91,338,000
Unrealized gains	1,228,000	424,000
Unrealized losses	0	482,000
Estimated fair value	82,234,000	91,280,000
Investment securities with unrealized losses [Abstract]
Unrealized Loss Position, Less Than 12 Months, Fair Value	0	40,741,000
Unrealized Loss Position, Less Than 12 Months, Unrealized Losses	0	(482,000)
Unrealized Loss Position, Less Than 12 Months, Number of Positions	0	4
Unrealized Loss Position, 12 Months or Longer, Fair Value	0	0
Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	0	0
Unrealized Loss Position, 12 Months or Longer, Number of Positions	0	0
Unrealized Loss Position, Total, Fair Value	0	40,741,000
Unrealized Loss Position, Total, Unrealized Losses	0	(482,000)
Unrealized Loss Position, Total, Number of Positions	0	4
Federal Agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	254,983,000	350,641,000
Unrealized gains	879,000	1,905,000
Unrealized losses	16,000	2,796,000
Estimated fair value	255,846,000	349,750,000
Investment securities with unrealized losses [Abstract]
Unrealized Loss Position, Less Than 12 Months, Fair Value	34,996,000	147,012,000
Unrealized Loss Position, Less Than 12 Months, Unrealized Losses	(16,000)	(2,796,000)
Unrealized Loss Position, Less Than 12 Months, Number of Positions	3	12
Unrealized Loss Position, 12 Months or Longer, Fair Value	0	0
Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	0	0
Unrealized Loss Position, 12 Months or Longer, Number of Positions	0	0
Unrealized Loss Position, Total, Fair Value	34,996,000	147,012,000
Unrealized Loss Position, Total, Unrealized Losses	(16,000)	(2,796,000)
Unrealized Loss Position, Total, Number of Positions	3	12
State & municipal [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	99,176,000	113,821,000
Unrealized gains	5,624,000	1,771,000
Unrealized losses	11,000	655,000
Estimated fair value	104,789,000	114,937,000
Investment securities with unrealized losses [Abstract]
Unrealized Loss Position, Less Than 12 Months, Fair Value	957,000	22,273,000
Unrealized Loss Position, Less Than 12 Months, Unrealized Losses	(10,000)	(317,000)
Unrealized Loss Position, Less Than 12 Months, Number of Positions	3	31
Unrealized Loss Position, 12 Months or Longer, Fair Value	377,000	7,533,000
Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	(1,000)	(338,000)
Unrealized Loss Position, 12 Months or Longer, Number of Positions	2	19
Unrealized Loss Position, Total, Fair Value	1,334,000	29,806,000
Unrealized Loss Position, Total, Unrealized Losses	(11,000)	(655,000)
Unrealized Loss Position, Total, Number of Positions	5	50
Mortgage-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	310,767,000	233,861,000
Unrealized gains	14,629,000	11,666,000
Unrealized losses	0	719,000
Estimated fair value	325,396,000	244,808,000
Investment securities with unrealized losses [Abstract]
Unrealized Loss Position, Less Than 12 Months, Fair Value	0	44,340,000
Unrealized Loss Position, Less Than 12 Months, Unrealized Losses	0	(719,000)
Unrealized Loss Position, Less Than 12 Months, Number of Positions	0	3
Unrealized Loss Position, 12 Months or Longer, Fair Value	0	0
Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	0	0
Unrealized Loss Position, 12 Months or Longer, Number of Positions	0	0
Unrealized Loss Position, Total, Fair Value	0	44,340,000
Unrealized Loss Position, Total, Unrealized Losses	0	(719,000)
Unrealized Loss Position, Total, Number of Positions	0	3
Corporate [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	0	20,005,000
Unrealized gains	0	484,000
Unrealized losses	0	0
Estimated fair value	0	20,489,000
Other securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	8,935,000	8,059,000
Unrealized gains	2,021,000	2,162,000
Unrealized losses	76,000	5,000
Estimated fair value	10,880,000	10,216,000
Investment securities with unrealized losses [Abstract]
Unrealized Loss Position, Less Than 12 Months, Fair Value	645,000	95,000
Unrealized Loss Position, Less Than 12 Months, Unrealized Losses	(76,000)	(5,000)
Unrealized Loss Position, Less Than 12 Months, Number of Positions	2	1
Unrealized Loss Position, 12 Months or Longer, Fair Value	0	0
Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	0	0
Unrealized Loss Position, 12 Months or Longer, Number of Positions	0	0
Unrealized Loss Position, Total, Fair Value	645,000	95,000
Unrealized Loss Position, Total, Unrealized Losses	(76,000)	(5,000)
Unrealized Loss Position, Total, Number of Positions	2	1
Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	459,067,000	293,565,000
Unrealized gains	6,458,000	6,574,000
Unrealized losses	51,000	2,251,000
Estimated fair value	465,474,000	297,888,000
Investment securities with unrealized losses [Abstract]
Unrealized Loss Position, Less Than 12 Months, Fair Value	27,368,000	72,595,000
Unrealized Loss Position, Less Than 12 Months, Unrealized Losses	(51,000)	(2,251,000)
Unrealized Loss Position, Less Than 12 Months, Number of Positions	3	3
Unrealized Loss Position, 12 Months or Longer, Fair Value	0	0
Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	0	0
Unrealized Loss Position, 12 Months or Longer, Number of Positions	0	0
Unrealized Loss Position, Total, Fair Value	27,368,000	72,595,000
Unrealized Loss Position, Total, Unrealized Losses	$ (51,000)	$ (2,251,000)
Unrealized Loss Position, Total, Number of Positions	3	3