Securities (Details) (USD $)	9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 1,159,203,000	$ 1,213,934,000
Unrealized gains	31,983,000	30,839,000
Unrealized losses	79,000	154,000
Estimated fair value	1,191,107,000	1,244,619,000
Amortized cost of mortgage-backed securities comprised of Government Sponsored Enterprise Securities	246,600,000	290,200,000
Fair value of mortgage-backed securities comprised of Government Sponsored Enterprise Securities	260,300,000	303,000,000
Amortized cost of mortgage-backed securities comprised of US Government Agency Securities	17,500,000	20,500,000
Fair value of mortgage-backed securities comprised of US Government Agency Securities	19,300,000	22,400,000
Amortized cost of collateralized mortgage obligations comprised of Government Sponsored Enterprise Securities	387,500,000	398,300,000
Fair value of collateralized mortgage obligations comprised of Government Sponsored Enterprise Securities	394,200,000	402,400,000
Amortized cost of collateralized mortgage obligations comprised of US Government Agency Securities	50,900,000	60,800,000
Fair value of collateralized mortgage obligations comprised of US Government Agency Securities	52,700,000	63,100,000
Proceeds from sales of securities available for sale	1,800,000
Gains on sales of securities available for sale	400,000
Amortized costs of securities available for sale pledged to secure public deposits	1,200,000,000	1,200,000,000
Amortized costs of securities available for sale pledged as collateral for repurchase agreements	210,400,000	141,700,000
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	0	63,966,000
12 Months or Longer, Fair Value	169,000	377,000
Total, Fair Value	169,000	64,343,000
Unrealized Loss Position, Unrealized Losses [Abstract]
Less Than 12 Months, Unrealized Losses	0	(153,000)
12 Months or Longer, Unrealized Losses	(79,000)	(1,000)
Total, Unrealized Losses	(79,000)	(154,000)
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions	0	11
12 Months or Longer, Number of Positions	1	2
Total, Number of Positions	1	13
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis [Abstract]
Within One Year	26,616,000
From One to Five Years	262,685,000
From Five to Ten Years	273,272,000
After Ten years	587,919,000
Total, Amortized Cost	1,150,492,000
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Within One Year	26,807,000
From One to Five Years	265,541,000
From Five to Ten Years	282,328,000
After Ten Years	605,131,000
Total, Fair Value	1,179,807,000
Consolidated stockholders' equity threshold percentage that no single issuer of securities exceeded except for U.S. Government securities. (in hundredths)	10.00%
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	61,302,000	70,811,000
Unrealized gains	1,099,000	1,387,000
Unrealized losses	0	0
Estimated fair value	62,401,000	72,198,000
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Within One Year	24,501,000
From One to Five Years	27,735,000
From Five to Ten Years	6,380,000
After Ten Years	2,686,000
Securities held to maturity	61,302,000	70,811,000
Held-to-maturity Securities, Debt Maturities, Fair Value [Abstract]
Within One Year	24,577,000
From One to Five Years	28,476,000
From Five to Ten Years	6,459,000
After Ten Years	2,889,000
Total, Fair Value	62,401,000
Mortgage-backed [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	1,252,000	1,447,000
Unrealized gains	203,000	213,000
Unrealized losses	0	0
Estimated fair value	1,455,000	1,660,000
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Securities held to maturity	1,252,000	1,447,000
State & municipal [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	60,050,000	69,364,000
Unrealized gains	896,000	1,174,000
Unrealized losses	0	0
Estimated fair value	60,946,000	70,538,000
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Securities held to maturity	60,050,000	69,364,000
US Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	63,747,000	81,006,000
Unrealized gains	915,000	1,228,000
Unrealized losses	0	0
Estimated fair value	64,662,000	82,234,000
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	0	0
12 Months or Longer, Fair Value	0	0
Total, Fair Value	0	0
Unrealized Loss Position, Unrealized Losses [Abstract]
Less Than 12 Months, Unrealized Losses	0	0
12 Months or Longer, Unrealized Losses	0	0
Total, Unrealized Losses	0	0
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions	0	0
12 Months or Longer, Number of Positions	0	0
Total, Number of Positions	0	0
Federal Agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	294,503,000	254,983,000
Unrealized gains	1,655,000	879,000
Unrealized losses	0	16,000
Estimated fair value	296,158,000	255,846,000
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	0	34,996,000
12 Months or Longer, Fair Value	0	0
Total, Fair Value	0	34,996,000
Unrealized Loss Position, Unrealized Losses [Abstract]
Less Than 12 Months, Unrealized Losses	0	(16,000)
12 Months or Longer, Unrealized Losses	0	0
Total, Unrealized Losses	0	(16,000)
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions	0	3
12 Months or Longer, Number of Positions	0	0
Total, Number of Positions	0	3
State & municipal [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	87,786,000	99,176,000
Unrealized gains	4,718,000	5,624,000
Unrealized losses	0	11,000
Estimated fair value	92,504,000	104,789,000
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	0	957,000
12 Months or Longer, Fair Value	0	377,000
Total, Fair Value	0	1,334,000
Unrealized Loss Position, Unrealized Losses [Abstract]
Less Than 12 Months, Unrealized Losses	0	(10,000)
12 Months or Longer, Unrealized Losses	0	(1,000)
Total, Unrealized Losses	0	(11,000)
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions	0	3
12 Months or Longer, Number of Positions	0	2
Total, Number of Positions	0	5
Mortgage-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	264,073,000	310,767,000
Unrealized gains	15,523,000	14,629,000
Unrealized losses	0	0
Estimated fair value	279,596,000	325,396,000
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	0	0
12 Months or Longer, Fair Value	0	0
Total, Fair Value	0	0
Unrealized Loss Position, Unrealized Losses [Abstract]
Less Than 12 Months, Unrealized Losses	0	0
12 Months or Longer, Unrealized Losses	0	0
Total, Unrealized Losses	0	0
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions	0	0
12 Months or Longer, Number of Positions	0	0
Total, Number of Positions	0	0
Collateralized mortgage obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	440,383,000	459,067,000
Unrealized gains	6,504,000	6,458,000
Unrealized losses	0	51,000
Estimated fair value	446,887,000	465,474,000
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	0	27,368,000
12 Months or Longer, Fair Value	0	0
Total, Fair Value	0	27,368,000
Unrealized Loss Position, Unrealized Losses [Abstract]
Less Than 12 Months, Unrealized Losses	0	(51,000)
12 Months or Longer, Unrealized Losses	0	0
Total, Unrealized Losses	0	(51,000)
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions	0	3
12 Months or Longer, Number of Positions	0	0
Total, Number of Positions	0	3
Other securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	8,711,000	8,935,000
Unrealized gains	2,668,000	2,021,000
Unrealized losses	79,000	76,000
Estimated fair value	11,300,000	10,880,000
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	0	645,000
12 Months or Longer, Fair Value	169,000	0
Total, Fair Value	169,000	645,000
Unrealized Loss Position, Unrealized Losses [Abstract]
Less Than 12 Months, Unrealized Losses	0	(76,000)
12 Months or Longer, Unrealized Losses	(79,000)	0
Total, Unrealized Losses	$ (79,000)	$ (76,000)
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions	0	2
12 Months or Longer, Number of Positions	1	0
Total, Number of Positions	1	2