Loans and Allowance for Loan Losses (Details 3) (Acquired loans, USD $)	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2013 FASB ASC Topic 310-30	Dec. 31, 2012 FASB ASC Topic 310-30	Mar. 31, 2012 FASB ASC Topic 310-30	Mar. 31, 2013 FASB ASC Topic 310-20 Loans	Dec. 31, 2012 FASB ASC Topic 310-20 Loans	Mar. 31, 2012 FASB ASC Topic 310-20 Loans	Dec. 13, 2012 Savannah Bancorp ("SAVB")	Dec. 31, 2012 Savannah Bancorp ("SAVB") FASB ASC Topic 310-20 Loans	Apr. 24, 2012 Peoples FASB ASC Topic 310-30	Mar. 31, 2013 Loans Impaired at Acquisition	Dec. 31, 2012 Loans Impaired at Acquisition	Mar. 31, 2012 Loans Impaired at Acquisition	Mar. 31, 2013 Loans Impaired at Acquisition FASB ASC Topic 310-30	Dec. 31, 2012 Loans Impaired at Acquisition FASB ASC Topic 310-30	Mar. 31, 2012 Loans Impaired at Acquisition FASB ASC Topic 310-30	Dec. 13, 2012 Loans Impaired at Acquisition Savannah Bancorp ("SAVB") FASB ASC Topic 310-30	Apr. 24, 2012 Loans Impaired at Acquisition Peoples FASB ASC Topic 310-30	Mar. 31, 2013 Loans Not Impaired at Acquisition	Dec. 31, 2012 Loans Not Impaired at Acquisition	Mar. 31, 2012 Loans Not Impaired at Acquisition	Mar. 31, 2013 Loans Not Impaired at Acquisition FASB ASC Topic 310-30	Dec. 31, 2012 Loans Not Impaired at Acquisition FASB ASC Topic 310-30	Mar. 31, 2012 Loans Not Impaired at Acquisition FASB ASC Topic 310-30	Dec. 13, 2012 Loans Not Impaired at Acquisition Savannah Bancorp ("SAVB") FASB ASC Topic 310-30	Apr. 24, 2012 Loans Not Impaired at Acquisition Peoples FASB ASC Topic 310-30
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Contractual principal and interest	$ 1,183,432,000	$ 1,303,047,000	$ 612,295,000								$ 638,875,000		$ 306,963,000				$ 336,815,000	$ 376,894,000	$ 282,499,000	$ 155,582,000	$ 56,940,000				$ 846,617,000	$ 926,153,000	$ 329,796,000	$ 483,293,000	$ 250,023,000
Non-accretable difference	(108,890,000)	(140,671,000)	(157,001,000)								(46,952,000)		(37,797,000)				(68,127,000)	(86,514,000)	(100,477,000)	(37,492,000)	(21,237,000)				(40,763,000)	(54,157,000)	(56,524,000)	(9,460,000)	(16,560,000)
Cash flows expected to be collected	1,074,542,000	1,162,376,000	455,294,000								591,923,000		269,166,000				268,688,000	290,380,000	182,022,000	118,090,000	35,703,000				805,854,000	871,996,000	273,272,000	473,833,000	233,463,000
Accretable yield	(149,521,000)	(160,849,000)	(86,150,000)								(60,081,000)		(34,921,000)				(49,659,000)	(48,411,000)	(30,720,000)	(8,615,000)	(4,968,000)				(99,862,000)	(112,438,000)	(55,430,000)	(51,466,000)	(29,953,000)
Total acquired loans	995,255,000	1,074,742,000	369,144,000		925,021,000	1,001,527,000	369,144,000	70,234,000	73,215,000	73,215,000	531,842,000	69,500,000	234,245,000	219,029,000	241,969,000	151,302,000	219,029,000	241,969,000	151,302,000	109,475,000	30,735,000	776,226,000	832,773,000	217,842,000	705,992,000	759,558,000	217,842,000	422,367,000	203,510,000
Allowance for loan losses on acquired loans	(31,277,000)	(32,132,000)	(34,355,000)	(31,620,000)	(31,277,000)	(32,132,000)	(34,355,000)							(26,302,000)	(24,988,000)	(25,712,000)	(26,302,000)	(24,988,000)	(25,712,000)			(4,975,000)	(7,144,000)	(8,643,000)	(4,975,000)	(7,144,000)	(8,643,000)
Contractual principal								75,200,000	78,500,000			74,900,000
Discount								4,900,000	5,300,000			5,400,000
Unpaid principal balance for acquired loans	$ 1,200,000,000	$ 1,300,000,000	$ 540,400,000