Parent Company Only Financial Information (Details 3) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash Flows from Operating Activities
Net income	$ 4,917,000	$ 4,909,000	$ 4,888,000	$ 7,643,000	$ 5,746,000	$ 7,570,000	$ 7,447,000	$ 9,110,000	$ 22,357,000	$ 29,873,000	$ 23,230,000
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization									8,759,000	9,063,000	10,278,000
Stock-based compensation									991,000	488,000	194,000
Fair value adjustment on employee stock ownership plan shares allocated									(322,000)	(318,000)	(328,000)
Change in assets and liabilities:
Decrease in other assets									8,368,000	7,745,000	34,559,000
Increase (decrease) in other liabilities									992,000	(4,033,000)	(5,290,000)
Net cash provided by operating activities									49,069,000	115,878,000	87,770,000
Cash Flows from Investing Activities
Decrease in loans									(33,680,000)	233,901,000	362,472,000
Proceeds from sales of premises and equipment									77,000	1,043,000	157,000
Purchases of premises and equipment									(8,611,000)	(2,748,000)	(2,037,000)
Net cash (used in) provided by investing activities									(204,435,000)	13,241,000	351,982,000
Cash Flows from Financing Activities
Principal payments on long-term debt									(12,000,000)	(23,325,000)	(38,500,000)
Repurchase of Series T Preferred stock										(100,000,000)
Proceeds from issuance of Series C Preferred stock										72,664,000
Proceeds from issuance of Series B Preferred stock, net											31,862,000
Proceeds from issuance of Common stock, net											52,454,000
Cash dividends paid									(24,427,000)	(18,343,000)	(15,617,000)
Net cash provided by (used in) financing activities									191,568,000	(233,031,000)	(227,858,000)
Cash and due from banks, beginning				315,053,000				418,965,000	315,053,000	418,965,000	207,071,000
Cash and due from banks, ending	351,255,000				315,053,000				351,255,000	315,053,000	418,965,000
Parent
Cash Flows from Operating Activities
Net income									22,357,000	29,873,000	23,230,000
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization									98,000	120,000	310,000
Distributions less than net income of subsidiaries									(20,960,000)	(29,286,000)	(24,434,000)
Stock-based compensation									991,000	488,000	194,000
Fair value adjustment on employee stock ownership plan shares allocated									(322,000)	(318,000)	(328,000)
Change in assets and liabilities:
Decrease in other assets									125,000	1,479,000	(953,000)
Increase (decrease) in other liabilities									1,435,000	(22,630,000)	22,128,000
Net cash provided by operating activities									3,724,000	(20,274,000)	20,147,000
Cash Flows from Investing Activities
Securities purchased under agreements to resell, net										10,909,000	16,095,000
Decrease in loans									95,000	85,000	81,000
Proceeds from sales of premises and equipment											191,000
Purchases of premises and equipment									(11,000)	(5,000)	(6,000)
Investment in subsidiary, net											(12,500,000)
Net cash (used in) provided by investing activities									84,000	10,989,000	3,861,000
Cash Flows from Financing Activities
Proceeds from short-term debt											4,000,000
Principal payments on long-term debt											(13,000,000)
Principal payments on short-term debt											(4,000,000)
Repurchase of Series T Preferred stock										(100,000,000)
Proceeds from issuance of Series C Preferred stock										72,664,000
Proceeds from issuance of Series B Preferred stock, net											31,862,000
Proceeds from issuance of Common stock, net											52,454,000
Cash dividends paid									(24,427,000)	(18,343,000)	(15,617,000)
Net cash provided by (used in) financing activities									(24,427,000)	(45,679,000)	55,699,000
Net (decrease) increase in cash and due from subsidiary banks									(20,619,000)	(54,964,000)	79,707,000
Cash and due from banks, beginning				25,771,000				80,735,000	25,771,000	80,735,000	1,028,000
Cash and due from banks, ending	$ 5,152,000				$ 25,771,000				$ 5,152,000	$ 25,771,000	$ 80,735,000