Securities (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2014 Position	Mar. 31, 2013	Dec. 31, 2013 Position
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 1,383,839,000		$ 1,379,751,000
Unrealized gains	15,357,000		14,737,000
Unrealized losses	21,611,000		29,607,000
Estimated fair value	1,377,585,000		1,364,881,000
Sales transactions of securities available for sale [Abstract]
Proceeds from sales	0	2,600,000
Gross realized gains	0	1,100,000
Loss on sales	0	0
Amortized costs of securities available for sale pledged to secure public deposits	1,500,000,000		1,400,000,000
Amortized costs of securities available for sale pledged as collateral for repurchase agreements	224,900,000		218,400,000
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	1,705,294,000		812,106,000
12 Months or Longer, Fair Value	72,477,000		9,842,000
Total, Fair Value	1,777,771,000		821,948,000
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months Unrealized Losses	(18,227,000)		(29,201,000)
12 months or longer Unrealized Losses	(3,384,000)		(406,000)
Total Unrealized Losses	(21,611,000)		(29,607,000)
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions	283		314
12 Months or Longer, Number of Positions	13		2
Total, Number of Positions	296		316
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	117,896,000		117,283,000
Unrealized gains	481,000		570,000
Unrealized losses	3,457,000		4,577,000
Estimated fair value	114,920,000		113,276,000
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	59,648,000		58,468,000
12 Months or Longer, Fair Value	0		0
Total, Fair Value	59,648,000		58,468,000
Unrealized Loss Position, Unrealized Losses [Abstract]
Less Than 12 Months, Unrealized Losses	(3,457,000)		(4,577,000)
12 Months or Longer, Unrealized Losses	0		0
Total, Unrealized Losses	(3,457,000)		(4,577,000)
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions	8		6
12 Months or Longer, Number of Positions	0		0
Total, Number of Positions	8		6
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	27,461,000
From one to five years	302,113,000
From five to ten years	259,225,000
After ten years	782,201,000
Total, Amortized Cost	1,371,000,000
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Within one year	27,627,000
From one to five years	301,603,000
From five to ten years	259,821,000
After ten years	773,080,000
Total, Fair Value	1,362,131,000
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Within one year	24,714,000
From one to five years	21,654,000
From five to ten years	8,401,000
After ten years	63,127,000
Securities held to maturity	117,896,000		117,283,000
Held-to-maturity Securities, Debt Maturities, Fair Value [Abstract]
Within one year	24,765,000
From one to five years	21,957,000
From five to ten years	8,395,000
After ten years	59,803,000
Total, Fair Value	114,920,000		113,276,000
State & Municipal [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	56,042,000		54,305,000
Unrealized gains	361,000		442,000
Unrealized losses	13,000		8,000
Estimated fair value	56,390,000		54,739,000
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	2,120,000		1,012,000
12 Months or Longer, Fair Value	0		0
Total, Fair Value	2,120,000		1,012,000
Unrealized Loss Position, Unrealized Losses [Abstract]
Less Than 12 Months, Unrealized Losses	(13,000)		(8,000)
12 Months or Longer, Unrealized Losses	0		0
Total, Unrealized Losses	(13,000)		(8,000)
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions	3		1
12 Months or Longer, Number of Positions	0		0
Total, Number of Positions	3		1
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Securities held to maturity	56,042,000		54,305,000
Held-to-maturity Securities, Debt Maturities, Fair Value [Abstract]
Total, Fair Value	56,390,000		54,739,000
Mortgage backed [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	881,000		953,000
Unrealized gains	120,000		128,000
Unrealized losses	0		0
Estimated fair value	1,001,000		1,081,000
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Securities held to maturity	881,000		953,000
Held-to-maturity Securities, Debt Maturities, Fair Value [Abstract]
Total, Fair Value	1,001,000		1,081,000
Collateralized Mortgage Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	60,973,000		62,025,000
Unrealized gains	0		0
Unrealized losses	3,444,000		4,569,000
Estimated fair value	57,529,000		57,456,000
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	57,528,000		57,456,000
12 Months or Longer, Fair Value	0		0
Total, Fair Value	57,528,000		57,456,000
Unrealized Loss Position, Unrealized Losses [Abstract]
Less Than 12 Months, Unrealized Losses	(3,444,000)		(4,569,000)
12 Months or Longer, Unrealized Losses	0		0
Total, Unrealized Losses	(3,444,000)		(4,569,000)
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions	5		5
12 Months or Longer, Number of Positions	0		0
Total, Number of Positions	5		5
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Securities held to maturity	60,973,000		62,025,000
Held-to-maturity Securities, Debt Maturities, Fair Value [Abstract]
Total, Fair Value	57,529,000		57,456,000
US Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	33,204,000		43,279,000
Unrealized gains	269,000		337,000
Unrealized losses	0		0
Estimated fair value	33,473,000		43,616,000
Federal Agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	305,245,000		285,880,000
Unrealized gains	430,000		343,000
Unrealized losses	5,517,000		7,308,000
Estimated fair value	300,158,000		278,915,000
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	245,397,000		233,935,000
12 Months or Longer, Fair Value	9,704,000		9,619,000
Total, Fair Value	255,101,000		243,554,000
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months Unrealized Losses	(5,221,000)		(6,927,000)
12 months or longer Unrealized Losses	(296,000)		(381,000)
Total Unrealized Losses	(5,517,000)		(7,308,000)
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions	21		20
12 Months or Longer, Number of Positions	1		1
Total, Number of Positions	22		21
Mortgage-Backed [Member]
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	1,110,605,000		143,080,000
12 Months or Longer, Fair Value	960,000		0
Total, Fair Value	1,111,565,000		143,080,000
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months Unrealized Losses	(1,465,000)		(2,216,000)
12 months or longer Unrealized Losses	(10,000)		0
Total Unrealized Losses	(1,475,000)		(2,216,000)
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions	58		79
12 Months or Longer, Number of Positions	4		0
Total, Number of Positions	62		79
Mortgage-Backed [Member] | Government-sponsored enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	351,748,000		337,666,000
Unrealized gains	6,164,000		5,788,000
Unrealized losses	1,404,000		2,131,000
Estimated fair value	356,508,000		341,323,000
Mortgage-Backed [Member] | U.S. government agency securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	20,781,000		21,924,000
Unrealized gains	940,000		1,002,000
Unrealized losses	71,000		85,000
Estimated fair value	21,650,000		22,841,000
State & Municipal [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	111,583,000		113,435,000
Unrealized gains	1,967,000		1,842,000
Unrealized losses	855,000		1,612,000
Estimated fair value	112,695,000		113,665,000
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	48,377,000		50,328,000
12 Months or Longer, Fair Value	934,000		0
Total, Fair Value	49,311,000		50,328,000
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months Unrealized Losses	(839,000)		(1,612,000)
12 months or longer Unrealized Losses	(16,000)		0
Total Unrealized Losses	(855,000)		(1,612,000)
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions	171		177
12 Months or Longer, Number of Positions	3		0
Total, Number of Positions	174		177
Collateralized Mortgage Obligations [Member]
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	295,408,000		379,273,000
12 Months or Longer, Fair Value	60,681,000		0
Total, Fair Value	356,089,000		379,273,000
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months Unrealized Losses	(10,516,000)		(18,243,000)
12 months or longer Unrealized Losses	(3,012,000)		0
Total Unrealized Losses	(13,528,000)		(18,243,000)
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions	31		36
12 Months or Longer, Number of Positions	4		0
Total, Number of Positions	35		36
Collateralized Mortgage Obligations [Member] | Government-sponsored enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	501,563,000		521,257,000
Unrealized gains	2,080,000		1,777,000
Unrealized losses	13,411,000		18,141,000
Estimated fair value	490,232,000		504,893,000
Collateralized Mortgage Obligations [Member] | U.S. government agency securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	46,876,000		43,943,000
Unrealized gains	656,000		794,000
Unrealized losses	117,000		102,000
Estimated fair value	47,415,000		44,635,000
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	12,839,000		12,367,000
Unrealized gains	2,851,000		2,854,000
Unrealized losses	236,000		228,000
Estimated fair value	15,454,000		14,993,000
Unrealized Loss Position, Fair Value [Abstract]
Less Than 12 Months, Fair Value	5,507,000		5,490,000
12 Months or Longer, Fair Value	198,000		223,000
Total, Fair Value	5,705,000		5,713,000
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months Unrealized Losses	(186,000)		(203,000)
12 months or longer Unrealized Losses	(50,000)		(25,000)
Total Unrealized Losses	$ (236,000)		$ (228,000)
Unrealized Loss Position, Number of Positions [Abstract]
Less Than 12 Months, Number of Positions	2		2
12 Months or Longer, Number of Positions	1		1
Total, Number of Positions	3		3