Business Combinations, BancTrust Financial Group (Details) (USD $)	12 Months Ended			0 Months Ended	3 Months Ended		9 Months Ended	12 Months Ended
	Dec. 31, 2013	Sep. 30, 2014	Sep. 30, 2013	Feb. 15, 2013 BancTrust Financial Group, Inc. [Member]	Mar. 31, 2014 BancTrust Financial Group, Inc. [Member]	Mar. 31, 2013 BancTrust Financial Group, Inc. [Member]	Sep. 30, 2014 BancTrust Financial Group, Inc. [Member] Market	Dec. 31, 2013 BancTrust Financial Group, Inc. [Member]
Business Acquisition [Line Items]
Age of acquired entity				26 years
Preferred stock and warrants repurchased				$ 50,000,000
Issued value of preferred stock associated warrant under capital purchase program				52,600,000
Equity issued, per share of acquired company (in shares)				0.125
Decrease in acquired non covered loans as measurement period adjustment	6,800,000							6,800,000
Decrease in Premises and equipment as measurement period adjustment								627,000
Decrease in other real estate as measurement period adjustment								2,600,000
Increase in deferred tax asset as measurement period adjustment								3,400,000
Increase in goodwill as measurement period adjustment								6,300,000
Transfer to other real estate as measurement period adjustment								1,600,000
Decrease in goodwill with a corresponding increase in the deferred tax asset as a measurement period adjustment					7,400,000
Assets [Abstract]
Cash and due from banks				141,616,000
Securities available for sale				528,016,000
Loans held for sale				1,050,000
Acquired noncovered loans				944,235,000
Premises and equipment, net				54,952,000
Identifiable intangible assets				33,498,000
Other real estate				40,103,000
Other assets				109,423,000
Total Assets		0	1,845,930,000	1,852,893,000
Liabilities [Abstract]
Deposits				1,740,254,000
Other borrowings				64,051,000
Other liabilities				16,761,000
Total Liabilities		0	1,821,066,000	1,821,066,000
Net identified assets acquired at fair value				31,827,000
Goodwill	372,851,000	365,500,000		74,247,000
Net assets acquired at fair value				106,074,000
Equity issued (in shares)				2,240,000
Business acquisition, equity issued, value assigned				53,500,000
Business acquisition, closing stock price (in dollars per share)				$ 23.83
Number of markets entered due to acquisition							15
Amortization period of acquired intangible asset							10 years
Business acquisition, total transaction expenses						9,400,000
Business acquisition, severance expense						1,400,000
Business acquisition, contract termination and other expenses						$ 7,900,000