Securities (Details) (USD $)	9 Months Ended		12 Months Ended
	Sep. 30, 2013 Position	Sep. 30, 2012	Dec. 31, 2012 Position
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 1,392,923,000		$ 1,120,384,000
Unrealized gains	16,886,000		27,794,000
Unrealized losses	24,075,000		179,000
Estimated fair value	1,385,734,000		1,147,999,000
Sales transactions of securities available for sale [Abstract]
Proceeds from sales	27,600,000	1,800,000
Gross realized gains	1,400,000	600,000
Loss on sales	0	0
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	222,200,000		209,000,000
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	1,342,704,000		40,397,000
12 Months or Longer, Fair Value	218,000		167,000
Total, Fair Value	1,342,922,000		40,564,000
Unrealized Loss Position, Unrealized Losses [Abstract]
Less Than 12 Months, Unrealized Losses	(24,045,000)		(97,000)
12 Months or Longer, Unrealized Losses	(30,000)		(82,000)
Total, Unrealized Losses	(24,075,000)		(179,000)
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions	332		7
12 Months or Longer, Number of Positions	1		1
Total, Number of Positions	333		8
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	118,259,000		60,563,000
Unrealized gains	612,000		972,000
Unrealized losses	3,251,000		0
Estimated fair value	115,620,000		61,535,000
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	63,048,000
12 Months or Longer, Fair Value	0
Total, Fair Value	63,048,000
Unrealized Loss Position, Unrealized Losses [Abstract]
Less Than 12 Months, Unrealized Losses	(3,251,000)
12 Months or Longer, Unrealized Losses	0
Total, Unrealized Losses	(3,251,000)
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions	5
12 Months or Longer, Number of Positions	0
Total, Number of Positions	5
Consolidated stockholders' equity threshold percentage that no single issuer of securities exceeded except for U.S. Government securities. (in hundredths)	10.00%
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis [Abstract]
Within one year	26,527,000
From one to five years	272,953,000
From five to ten years	295,191,000
After ten years	785,885,000
Total, Amortized Cost	1,380,556,000
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Within one year	26,704,000
From one to five years	274,104,000
From five to ten years	293,558,000
After ten years	776,650,000
Total, Fair Value	1,371,016,000
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Within one year	25,305,000
From one to five years	22,364,000
From five to ten years	5,054,000
After ten years	65,536,000
Securities held to maturity	118,259,000		60,563,000
Held-to-maturity Securities, Debt Maturities, Fair Value [Abstract]
Within one year	25,412,000
From one to five years	22,744,000
From five to ten years	5,059,000
After ten years	62,405,000
Total, Fair Value	115,620,000		61,535,000
State & Municipal [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	54,228,000		59,395,000
Unrealized gains	490,000		788,000
Unrealized losses	0		0
Estimated fair value	54,718,000		60,183,000
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Securities held to maturity	54,228,000		59,395,000
Held-to-maturity Securities, Debt Maturities, Fair Value [Abstract]
Total, Fair Value	54,718,000		60,183,000
Mortgage backed [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	983,000		1,168,000
Unrealized gains	122,000		184,000
Unrealized losses	0		0
Estimated fair value	1,105,000		1,352,000
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Securities held to maturity	983,000		1,168,000
Held-to-maturity Securities, Debt Maturities, Fair Value [Abstract]
Total, Fair Value	1,105,000		1,352,000
Collateralized Mortgage Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	63,048,000
Unrealized gains	0
Unrealized losses	3,251,000
Estimated fair value	59,797,000
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	63,048,000
12 Months or Longer, Fair Value	0
Total, Fair Value	63,048,000
Unrealized Loss Position, Unrealized Losses [Abstract]
Less Than 12 Months, Unrealized Losses	(3,251,000)
12 Months or Longer, Unrealized Losses	0
Total, Unrealized Losses	(3,251,000)
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions	5
12 Months or Longer, Number of Positions	0
Total, Number of Positions	5
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Securities held to maturity	63,048,000
Held-to-maturity Securities, Debt Maturities, Fair Value [Abstract]
Total, Fair Value	59,797,000
US Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	43,359,000		63,668,000
Unrealized gains	445,000		757,000
Unrealized losses	0		0
Estimated fair value	43,804,000		64,425,000
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value			0
12 Months or Longer, Fair Value			0
Total, Fair Value			0
Unrealized Loss Position, Unrealized Losses [Abstract]
Less Than 12 Months, Unrealized Losses			0
12 Months or Longer, Unrealized Losses			0
Total, Unrealized Losses			0
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions			0
12 Months or Longer, Number of Positions			0
Total, Number of Positions			0
Federal Agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	300,964,000		281,398,000
Unrealized gains	369,000		1,507,000
Unrealized losses	6,139,000		91,000
Estimated fair value	295,194,000		282,814,000
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	300,964,000		39,906,000
12 Months or Longer, Fair Value	0		0
Total, Fair Value	300,964,000		39,906,000
Unrealized Loss Position, Unrealized Losses [Abstract]
Less Than 12 Months, Unrealized Losses	(6,139,000)		(91,000)
12 Months or Longer, Unrealized Losses	0		0
Total, Unrealized Losses	(6,139,000)		(91,000)
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions	20		4
12 Months or Longer, Number of Positions	0		0
Total, Number of Positions	20		4
Mortgage-Backed [Member]
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	327,504,000		0
12 Months or Longer, Fair Value	0		0
Total, Fair Value	327,504,000		0
Unrealized Loss Position, Unrealized Losses [Abstract]
Less Than 12 Months, Unrealized Losses	(1,046,000)		0
12 Months or Longer, Unrealized Losses	0		0
Total, Unrealized Losses	(1,046,000)		0
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions	81		0
12 Months or Longer, Number of Positions	0		0
Total, Number of Positions	81		0
Mortgage-Backed [Member] | Government-sponsored enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	303,907,000		221,110,000
Unrealized gains	7,652,000		11,175,000
Unrealized losses	960,000		0
Estimated fair value	310,599,000		232,285,000
Mortgage-Backed [Member] | U.S. government securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	23,613,000		16,351,000
Unrealized gains	1,080,000		1,645,000
Unrealized losses	86,000		0
Estimated fair value	24,607,000		17,996,000
State & Municipal [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	117,936,000		82,675,000
Unrealized gains	2,083,000		4,127,000
Unrealized losses	1,417,000		0
Estimated fair value	118,602,000		86,802,000
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	117,936,000		0
12 Months or Longer, Fair Value	0		0
Total, Fair Value	117,936,000		0
Unrealized Loss Position, Unrealized Losses [Abstract]
Less Than 12 Months, Unrealized Losses	(1,417,000)		0
12 Months or Longer, Unrealized Losses	0		0
Total, Unrealized Losses	(1,417,000)		0
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions	189		0
12 Months or Longer, Number of Positions	0		0
Total, Number of Positions	189		0
Collateralized Mortgage Obligations [Member]
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	590,777,000		23,000
12 Months or Longer, Fair Value	0		0
Total, Fair Value	590,777,000		23,000
Unrealized Loss Position, Unrealized Losses [Abstract]
Less Than 12 Months, Unrealized Losses	(15,273,000)		0
12 Months or Longer, Unrealized Losses	0		0
Total, Unrealized Losses	(15,273,000)		0
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions	40		2
12 Months or Longer, Number of Positions	0		0
Total, Number of Positions	40		2
Collateralized Mortgage Obligations [Member] | Government-sponsored enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	543,447,000		399,147,000
Unrealized gains	1,792,000		4,418,000
Unrealized losses	15,211,000		0
Estimated fair value	530,028,000		403,565,000
Collateralized Mortgage Obligations [Member] | U.S. government securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	47,330,000		44,825,000
Unrealized gains	914,000		1,333,000
Unrealized losses	62,000		0
Estimated fair value	48,182,000		46,158,000
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	12,367,000		11,210,000
Unrealized gains	2,551,000		2,832,000
Unrealized losses	200,000		88,000
Estimated fair value	14,718,000		13,954,000
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	5,523,000		468,000
12 Months or Longer, Fair Value	218,000		167,000
Total, Fair Value	5,741,000		635,000
Unrealized Loss Position, Unrealized Losses [Abstract]
Less Than 12 Months, Unrealized Losses	(170,000)		(6,000)
12 Months or Longer, Unrealized Losses	(30,000)		(82,000)
Total, Unrealized Losses	$ (200,000)		$ (88,000)
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions	2		1
12 Months or Longer, Number of Positions	1		1
Total, Number of Positions	3		2