Fair Value Part 3 (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity	$ 1,170,685,000	$ 1,168,728,000
Net LHFI	6,379,853,000	5,732,433,000
FDIC indemnification asset	6,997,000	14,347,000	21,774,000	28,348,000
Deposits	9,698,358,000	9,859,902,000
Long-term FHLB advances	1,253,000	8,458,000
Subordinated notes	49,936,000	49,904,000
Junior subordinated debt securities	61,856,000	61,856,000
Nonfinancial Assets and Liabilities [Abstract]
Outstanding balances in impaired loans	47,100,000	31,600,000
Foreclosed assets measured at fair value	37,400,000	80,300,000
Allowance for possible loan losses, Charge-offs	13,900,000	11,400,000
Foreclosed assets re-measured after initial recognition	48,700,000	53,800,000
Write-downs of Allowance for Foreclosed Assets after Initial Recognition	7,700,000	6,400,000
Estimated fair value of financial instruments with immediate and shorter-term maturities maximum	90 days
Noninterest income in Mortgage banking, net for changes in fair value of LHFS	2,000,000
Fair value and the contractual principal outstanding of the LHFS [Abstract]
Fair value of LHFS	91,182,000
LHFS contractual principal outstanding	88,106,000
Fair value less unpaid principal	3,076,000
BancTrust Financial Group, Inc. [Member]
Nonfinancial Assets and Liabilities [Abstract]
Foreclosed assets measured at fair value		40,100,000
Level 2 [Member] | Carrying Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and short-term investments	317,858,000	353,014,000
Securities held to maturity	1,170,685,000	1,168,728,000
Deposits	9,698,358,000	9,859,902,000
Short-term liabilities	868,620,000	317,972,000
Long-term FHLB advances	1,253,000	8,458,000
Subordinated notes	49,936,000	49,904,000
Junior subordinated debt securities	61,856,000	61,856,000
Level 2 [Member] | Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and short-term investments	317,858,000	353,014,000
Securities held to maturity	1,182,846,000	1,150,833,000
Deposits	9,702,864,000	9,866,118,000
Short-term liabilities	868,620,000	317,972,000
Long-term FHLB advances	1,263,000	8,474,000
Subordinated notes	53,504,000	53,387,000
Junior subordinated debt securities	46,392,000	40,206,000
Level 3 [Member] | Carrying Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net LHFI	6,379,853,000	5,732,433,000
Net acquired loans	537,350,000	794,570,000
FDIC indemnification asset	6,997,000	14,347,000
Level 3 [Member] | Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net LHFI	6,453,618,000	5,787,408,000
Net acquired loans	537,350,000	794,570,000
FDIC indemnification asset	$ 6,997,000	$ 14,347,000