Impaired Loans (Detail) (USD $)	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Sep. 30, 2012	Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	$ 170,743,000	$ 170,743,000	$ 125,331,000
Partial Charge-offs to Date	25,871,000	25,871,000	28,908,000
Recorded Investment	144,872,000	144,872,000	96,423,000
Related Allowance	33,756,000	33,756,000	7,315,000
Average Recorded Investment	125,317,000	118,761,000	103,872,000
Interest Income Recognized	1,034,000	1,155,000	903,000
Consumer Portfolio Segment
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	119,000	119,000	125,000
Partial Charge-offs to Date	0	0	6,000
Recorded Investment	119,000	119,000	119,000
Related Allowance	60,000	60,000	60,000
Average Recorded Investment	120,000	123,000	183,000
Interest Income Recognized	0	0	0
Commercial Portfolio Segment
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	154,981,000	154,981,000	107,962,000
Partial Charge-offs to Date	24,727,000	24,727,000	27,012,000
Recorded Investment	130,254,000	130,254,000	80,950,000
Related Allowance	30,633,000	30,633,000	4,985,000
Average Recorded Investment	110,194,000	103,642,000	87,628,000
Interest Income Recognized	986,000	1,093,000	808,000
Residential real estate
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	15,643,000	15,643,000	17,244,000
Partial Charge-offs to Date	1,144,000	1,144,000	1,890,000
Recorded Investment	14,499,000	14,499,000	15,354,000
Related Allowance	3,063,000	3,063,000	2,270,000
Average Recorded Investment	15,003,000	14,996,000	16,061,000
Interest Income Recognized	48,000	62,000	95,000
Impaired Financing Receivables with No Related Allowance
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	65,295,000	65,295,000	91,498,000
Partial Charge-offs to Date	15,095,000	15,095,000	25,624,000
Recorded Investment	50,200,000	50,200,000	65,874,000
Related Allowance	0	0	0
Average Recorded Investment	46,830,000	62,291,000	50,226,000
Interest Income Recognized	73,000	144,000	638,000
Impaired Financing Receivables with No Related Allowance | Commercial construction, land and land development
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	45,511,000	45,511,000	60,974,000
Partial Charge-offs to Date	13,410,000	13,410,000	21,233,000
Recorded Investment	32,101,000	32,101,000	39,741,000
Related Allowance	0	0	0
Average Recorded Investment	28,370,000	39,071,000	28,959,000
Interest Income Recognized	19,000	79,000	200,000
Impaired Financing Receivables with No Related Allowance | Other commercial real estate
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	12,527,000	12,527,000	18,073,000
Partial Charge-offs to Date	618,000	618,000	2,235,000
Recorded Investment	11,909,000	11,909,000	15,838,000
Related Allowance	0	0	0
Average Recorded Investment	11,656,000	14,396,000	11,180,000
Interest Income Recognized	45,000	53,000	372,000
Impaired Financing Receivables with No Related Allowance | Residential Construction
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	114,000	114,000	128,000
Partial Charge-offs to Date	0	0	0
Recorded Investment	114,000	114,000	128,000
Related Allowance	0	0	0
Average Recorded Investment	118,000	122,000	790,000
Interest Income Recognized	0	0	0
Impaired Financing Receivables with No Related Allowance | Residential Mortgage
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	6,312,000	6,312,000	11,492,000
Partial Charge-offs to Date	707,000	707,000	1,796,000
Recorded Investment	5,605,000	5,605,000	9,696,000
Related Allowance	0	0	0
Average Recorded Investment	6,215,000	8,141,000	8,645,000
Interest Income Recognized	9,000	12,000	59,000
Impaired Financing Receivables with No Related Allowance | Commercial, financial and agricultural
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	831,000	831,000	831,000
Partial Charge-offs to Date	360,000	360,000	360,000
Recorded Investment	471,000	471,000	471,000
Related Allowance	0	0	0
Average Recorded Investment	471,000	561,000	652,000
Interest Income Recognized	0	0	7,000
Impaired Financing Receivables with No Related Allowance | Consumer Portfolio Segment
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	0	0	0
Partial Charge-offs to Date	0	0	0
Recorded Investment	0	0	0
Related Allowance	0	0	0
Average Recorded Investment	0	0	0
Interest Income Recognized	0	0	0
Impaired Financing Receivables with Related Allowance
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	105,448,000	105,448,000	33,833,000
Partial Charge-offs to Date	10,776,000	10,776,000	3,284,000
Recorded Investment	94,672,000	94,672,000	30,549,000
Related Allowance	33,756,000	33,756,000	7,315,000
Average Recorded Investment	78,487,000	56,470,000	53,646,000
Interest Income Recognized	961,000	1,011,000	265,000
Impaired Financing Receivables with Related Allowance | Commercial construction, land and land development
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	79,433,000	79,433,000	23,668,000
Partial Charge-offs to Date	9,527,000	9,527,000	2,488,000
Recorded Investment	69,906,000	69,906,000	21,180,000
Related Allowance	26,083,000	26,083,000	4,446,000
Average Recorded Investment	57,076,000	40,921,000	41,023,000
Interest Income Recognized	799,000	819,000	156,000
Impaired Financing Receivables with Related Allowance | Other commercial real estate
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	10,218,000	10,218,000	2,798,000
Partial Charge-offs to Date	117,000	117,000	0
Recorded Investment	10,101,000	10,101,000	2,798,000
Related Allowance	2,925,000	2,925,000	333,000
Average Recorded Investment	8,994,000	5,893,000	4,562,000
Interest Income Recognized	46,000	65,000	68,000
Impaired Financing Receivables with Related Allowance | Residential Construction
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	370,000	370,000	369,000
Partial Charge-offs to Date	0	0	0
Recorded Investment	370,000	370,000	369,000
Related Allowance	120,000	120,000	11,000
Average Recorded Investment	370,000	369,000	441,000
Interest Income Recognized	0	0	0
Impaired Financing Receivables with Related Allowance | Residential Mortgage
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	8,847,000	8,847,000	5,255,000
Partial Charge-offs to Date	437,000	437,000	94,000
Recorded Investment	8,410,000	8,410,000	5,161,000
Related Allowance	2,943,000	2,943,000	2,259,000
Average Recorded Investment	8,300,000	6,364,000	6,185,000
Interest Income Recognized	39,000	50,000	36,000
Impaired Financing Receivables with Related Allowance | Commercial, financial and agricultural
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	6,461,000	6,461,000	1,618,000
Partial Charge-offs to Date	695,000	695,000	696,000
Recorded Investment	5,766,000	5,766,000	922,000
Related Allowance	1,625,000	1,625,000	206,000
Average Recorded Investment	3,627,000	2,800,000	1,252,000
Interest Income Recognized	77,000	77,000	5,000
Impaired Financing Receivables with Related Allowance | Consumer Portfolio Segment
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	119,000	119,000	125,000
Partial Charge-offs to Date	0	0	6,000
Recorded Investment	119,000	119,000	119,000
Related Allowance	60,000	60,000	60,000
Average Recorded Investment	120,000	123,000	183,000
Interest Income Recognized	$ 0	$ 0	$ 0