Securities (Details) (USD $)	12 Months Ended
	Dec. 31, 2014 Position	Dec. 31, 2013 Position	Dec. 31, 2012
Available-for-sale securities, fair value to amortized cost basis [Abstract]
Amortized cost	$ 1,001,718,000	$ 1,379,751,000
Unrealized gains	14,823,000	14,737,000
Unrealized losses	3,370,000	29,607,000
Estimated fair value	1,013,171,000	1,364,881,000
Available-for-sale securities in continuous unrealized loss position, fair value [Abstract]
Less than 12 months	143,428,000	812,106,000
12 months or longer	244,836,000	9,842,000
Total	388,264,000	821,948,000
Available-for-sale securities in continuous unrealized loss position, unrealized losses [Abstract]
Less than 12 months	(500,000)	(29,201,000)
12 months or longer	(2,870,000)	(406,000)
Total	(3,370,000)	(29,607,000)
Available-for-sale securities in continuous unrealized loss position, number of positions [Abstract]
Less than 12 months	59	314
12 months or longer	58	2
Total	117	316
Sales transactions of securities available for sale [Abstract]
Proceeds from sales	189,000	27,593,000	1,790,000
Gross realized gains	49,000	1,283,000	442,000
Gross realized losses	0	0	0
Net securities (losses) gains	49,000	1,283,000	442,000
Gains from calls on securities available for sale	100,000	100,000	200,000
Amortized costs of securities available for sale pledged to secure public deposits	1,400,000,000	1,400,000,000
Amortized costs of securities available for sale pledged as collateral for repurchase agreements	208,800,000
Held-to-maturity securities, fair value to amortized cost basis [Abstract]
Amortized cost	454,361,000	117,283,000
Unrealized gains	2,721,000	570,000
Unrealized losses	2,088,000	4,577,000
Total, Estimated Fair Value	454,994,000	113,276,000
Held-to-maturity securities in continuous unrealized loss position, fair value [Abstract]
Less than 12 months	69,566,000	58,468,000
12 months or longer	48,034,000	0
Total	117,600,000	58,468,000
Held-to-maturity securities in continuous unrealized loss position, unrealized losses [Abstract]
Less than 12 months	(165,000)	(4,577,000)
12 months or longer	(1,923,000)	0
Total	(2,088,000)	(4,577,000)
Held-to-maturity securities in continuous unrealized loss position, number of positions [Abstract]
Less than 12 months	112	6
12 months or longer	10	0
Total	122	6
Securities transferred from available for sale portfolio to held to maturity portfolio	340,000,000
Unrealized losses of securities available for sale portfolio before transfer to held to maturity portfolio	8,300,000
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis [Abstract]
Within one year	28,193,000
From one to five years	356,696,000
From five to ten years	160,816,000
After ten years	443,195,000
Total, Amortized Cost	988,900,000
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Within one year	28,310,000
From one to five years	356,107,000
From five to ten years	163,924,000
After ten years	449,110,000
Total, Fair Value	997,451,000
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Within one year	22,999,000
From one to five years	15,506,000
From five to ten years	87,326,000
After ten years	328,530,000
Amortized cost	454,361,000	117,283,000
Held-to-maturity Securities, Debt Maturities, Fair Value [Abstract]
Within one year	23,075,000
From one to five years	15,606,000
From five to ten years	87,640,000
After ten years	328,673,000
Total, Estimated Fair Value	454,994,000	113,276,000
Consolidated stockholders' equity threshold percentage that no single issuer of securities exceeded except for U.S. Government securities. (in hundredths)	10.00%	10.00%
Mortgage-Backed [Member]
Held-to-maturity securities, fair value to amortized cost basis [Abstract]
Amortized cost	755,000	953,000
Unrealized gains	113,000	128,000
Unrealized losses	0	0
Total, Estimated Fair Value	868,000	1,081,000
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Amortized cost	755,000	953,000
Held-to-maturity Securities, Debt Maturities, Fair Value [Abstract]
Total, Estimated Fair Value	868,000	1,081,000
State & Municipal [Member]
Held-to-maturity securities, fair value to amortized cost basis [Abstract]
Amortized cost	135,978,000	54,305,000
Unrealized gains	674,000	442,000
Unrealized losses	123,000	8,000
Total, Estimated Fair Value	136,529,000	54,739,000
Held-to-maturity securities in continuous unrealized loss position, fair value [Abstract]
Less than 12 months	43,514,000	1,012,000
12 months or longer	1,619,000	0
Total	45,133,000	1,012,000
Held-to-maturity securities in continuous unrealized loss position, unrealized losses [Abstract]
Less than 12 months	(116,000)	(8,000)
12 months or longer	(7,000)	0
Total	(123,000)	(8,000)
Held-to-maturity securities in continuous unrealized loss position, number of positions [Abstract]
Less than 12 months	110	1
12 months or longer	6	0
Total	116	1
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Amortized cost	135,978,000	54,305,000
Held-to-maturity Securities, Debt Maturities, Fair Value [Abstract]
Total, Estimated Fair Value	136,529,000	54,739,000
Collateralized Mortgage Obligations [Member]
Held-to-maturity securities, fair value to amortized cost basis [Abstract]
Amortized cost	317,628,000	62,025,000
Unrealized gains	1,934,000	0
Unrealized losses	1,965,000	4,569,000
Total, Estimated Fair Value	317,597,000	57,456,000
Held-to-maturity securities in continuous unrealized loss position, fair value [Abstract]
Less than 12 months	26,052,000	57,456,000
12 months or longer	46,415,000	0
Total	72,467,000	57,456,000
Held-to-maturity securities in continuous unrealized loss position, unrealized losses [Abstract]
Less than 12 months	(49,000)	(4,569,000)
12 months or longer	(1,916,000)	0
Total	(1,965,000)	(4,569,000)
Held-to-maturity securities in continuous unrealized loss position, number of positions [Abstract]
Less than 12 months	2	5
12 months or longer	4	0
Total	6	5
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Amortized cost	317,628,000	62,025,000
Held-to-maturity Securities, Debt Maturities, Fair Value [Abstract]
Total, Estimated Fair Value	317,597,000	57,456,000
US Treasury [Member]
Available-for-sale securities, fair value to amortized cost basis [Abstract]
Amortized cost	23,041,000	43,279,000
Unrealized gains	70,000	337,000
Unrealized losses	0	0
Estimated fair value	23,111,000	43,616,000
Federal Agency [Member]
Available-for-sale securities, fair value to amortized cost basis [Abstract]
Amortized cost	332,193,000	285,880,000
Unrealized gains	327,000	343,000
Unrealized losses	2,606,000	7,308,000
Estimated fair value	329,914,000	278,915,000
Available-for-sale securities in continuous unrealized loss position, fair value [Abstract]
Less than 12 months	66,528,000	233,935,000
12 months or longer	198,151,000	9,619,000
Total	264,679,000	243,554,000
Available-for-sale securities in continuous unrealized loss position, unrealized losses [Abstract]
Less than 12 months	(226,000)	(6,927,000)
12 months or longer	(2,380,000)	(381,000)
Total	(2,606,000)	(7,308,000)
Available-for-sale securities in continuous unrealized loss position, number of positions [Abstract]
Less than 12 months	8	20
12 months or longer	16	1
Total	24	21
State & Municipal [Member]
Available-for-sale securities, fair value to amortized cost basis [Abstract]
Amortized cost	37,035,000	113,435,000
Unrealized gains	587,000	1,842,000
Unrealized losses	52,000	1,612,000
Estimated fair value	37,570,000	113,665,000
Available-for-sale securities in continuous unrealized loss position, fair value [Abstract]
Less than 12 months	8,818,000	50,328,000
12 months or longer	1,321,000	0
Total	10,139,000	50,328,000
Available-for-sale securities in continuous unrealized loss position, unrealized losses [Abstract]
Less than 12 months	(42,000)	(1,612,000)
12 months or longer	(10,000)	0
Total	(52,000)	(1,612,000)
Available-for-sale securities in continuous unrealized loss position, number of positions [Abstract]
Less than 12 months	33	177
12 months or longer	5	0
Total	38	177
Mortgage-Backed [Member]
Available-for-sale securities in continuous unrealized loss position, fair value [Abstract]
Less than 12 months	10,400,000	143,080,000
12 months or longer	35,565,000	0
Total	45,965,000	143,080,000
Available-for-sale securities in continuous unrealized loss position, unrealized losses [Abstract]
Less than 12 months	(36,000)	(2,216,000)
12 months or longer	(254,000)	0
Total	(290,000)	(2,216,000)
Available-for-sale securities in continuous unrealized loss position, number of positions [Abstract]
Less than 12 months	10	79
12 months or longer	31	0
Total	41	79
Mortgage-backed Securities, Issued by US Government-Sponsored Enterprises [Member]
Available-for-sale securities, fair value to amortized cost basis [Abstract]
Amortized cost	339,190,000	337,666,000
Unrealized gains	7,597,000	5,788,000
Unrealized losses	224,000	2,131,000
Estimated fair value	346,563,000	341,323,000
Mortgage-backed Securities, Issued by US Government Securities [Member]
Available-for-sale securities, fair value to amortized cost basis [Abstract]
Amortized cost	17,367,000	21,924,000
Unrealized gains	863,000	1,002,000
Unrealized losses	66,000	85,000
Estimated fair value	18,164,000	22,841,000
Collateralized Mortgage Obligations [Member]
Available-for-sale securities in continuous unrealized loss position, fair value [Abstract]
Less than 12 months	57,682,000	379,273,000
12 months or longer	6,598,000	0
Total	64,280,000	379,273,000
Available-for-sale securities in continuous unrealized loss position, unrealized losses [Abstract]
Less than 12 months	(196,000)	(18,243,000)
12 months or longer	(74,000)	0
Total	(270,000)	(18,243,000)
Available-for-sale securities in continuous unrealized loss position, number of positions [Abstract]
Less than 12 months	8	36
12 months or longer	4	0
Total	12	36
Collateralized Mortgage Obligations, Government-Sponsored Enterprises [Member]
Available-for-sale securities, fair value to amortized cost basis [Abstract]
Amortized cost	199,837,000	521,257,000
Unrealized gains	1,828,000	1,777,000
Unrealized losses	234,000	18,141,000
Estimated fair value	201,431,000	504,893,000
Collateralized Mortgage Obligations, U.S. Government Securities [Member]
Available-for-sale securities, fair value to amortized cost basis [Abstract]
Amortized cost	40,237,000	43,943,000
Unrealized gains	497,000	794,000
Unrealized losses	36,000	102,000
Estimated fair value	40,698,000	44,635,000
Other Securities [Member]
Available-for-sale securities, fair value to amortized cost basis [Abstract]
Amortized cost	12,818,000	12,367,000
Unrealized gains	3,054,000	2,854,000
Unrealized losses	152,000	228,000
Estimated fair value	15,720,000	14,993,000
Available-for-sale securities in continuous unrealized loss position, fair value [Abstract]
Less than 12 months	0	5,490,000
12 months or longer	3,201,000	223,000
Total	3,201,000	5,713,000
Available-for-sale securities in continuous unrealized loss position, unrealized losses [Abstract]
Less than 12 months	0	(203,000)
12 months or longer	(152,000)	(25,000)
Total	$ (152,000)	$ (228,000)
Available-for-sale securities in continuous unrealized loss position, number of positions [Abstract]
Less than 12 months	0	2
12 months or longer	2	1
Total	2	3