Loans and Allowance for Loan Losses (Details 3) (USD $)	Jul. 26, 2013 First Financial FASB ASC Topic 310-20	Dec. 31, 2012 Savannah Bancorp ("SAVB") FASB ASC Topic 310-20	Sep. 30, 2013 Acquired loans	Jun. 30, 2013 Acquired loans	Dec. 31, 2012 Acquired loans	Sep. 30, 2012 Acquired loans	Jun. 30, 2012 Acquired loans	Dec. 31, 2011 Acquired loans	Sep. 30, 2013 Acquired loans FASB ASC Topic 310-30	Dec. 31, 2012 Acquired loans FASB ASC Topic 310-30	Sep. 30, 2012 Acquired loans FASB ASC Topic 310-30	Jul. 26, 2013 Acquired loans First Financial	Dec. 13, 2012 Acquired loans Savannah Bancorp ("SAVB")	Apr. 24, 2012 Acquired loans Peoples FASB ASC Topic 310-30	Jul. 26, 2013 Acquired loans Loans Impaired at Acquisition First Financial FASB ASC Topic 310-30	Dec. 13, 2012 Acquired loans Loans Impaired at Acquisition Savannah Bancorp ("SAVB") FASB ASC Topic 310-30	Apr. 24, 2012 Acquired loans Loans Impaired at Acquisition Peoples FASB ASC Topic 310-30	Jul. 26, 2013 Acquired loans Loans Not Impaired at Acquisition First Financial FASB ASC Topic 310-30	Dec. 13, 2012 Acquired loans Loans Not Impaired at Acquisition Savannah Bancorp ("SAVB") FASB ASC Topic 310-30	Apr. 24, 2012 Acquired loans 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
Unpaid principal balance for acquired loans	$ 69,500,000	$ 1,670,000,000	$ 3,300,000,000		$ 1,300,000,000	$ 744,400,000
Contractual principal and interest									1,942,403,000	1,303,047,000	742,092,000	951,996,000	638,875,000	306,963,000	713,236,000	155,582,000	56,940,000	238,760,000	483,293,000	250,023,000
Non-accretable difference									(262,313,000)	(140,671,000)	(113,755,000)	(156,852,000)	(46,952,000)	(37,797,000)	(131,320,000)	(37,492,000)	(21,237,000)	(25,532,000)	(9,460,000)	(16,560,000)
Cash flows expected to be collected									1,680,090,000	1,162,376,000	628,337,000	795,144,000	591,923,000	269,166,000	581,916,000	118,090,000	35,703,000	213,228,000	473,833,000	233,463,000
Accretable yield									(332,320,000)	(160,849,000)	(107,346,000)	(203,193,000)	(60,081,000)	(34,921,000)	(159,546,000)	(8,615,000)	(4,968,000)	(43,647,000)	(51,466,000)	(29,953,000)
Total acquired loans			3,013,103,000		1,074,742,000	520,991,000			1,347,770,000	1,001,527,000	520,991,000	591,951,000	531,842,000	234,245,000	422,370,000	109,475,000	30,735,000	169,581,000	422,367,000	203,510,000
Allowance for loan losses on acquired loans			(31,141,000)	(31,597,000)	(32,132,000)	(31,138,000)	(35,813,000)	(31,620,000)	(31,141,000)	(32,132,000)	(31,138,000)
Contractual principal	74,900,000	1,710,000,000
Fair value adjustment	$ 5,400,000	$ 40,600,000