Mergers and Acquisitions - (Details) $ in Thousands		Apr. 01, 2016 USD ($) branch shares	Jul. 01, 2015 USD ($) branch agreement shares	Sep. 01, 2013 USD ($) branch shares	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Mar. 31, 2015 USD ($)	Aug. 31, 2011 USD ($) trust	Feb. 04, 2011 USD ($) branch	Jul. 23, 2010 USD ($) branch
Business Acquisition [Line Items]
Goodwill resulting from merger					$ 449,425	$ 445,871	$ 274,705
Eligible losses covered (percent)					80.00%
Eligible recoveries covered (percent)					80.00%
Heritage Financial Group
Business Acquisition [Line Items]
Total Purchase Price			$ 295,444
Payment to stock option holders			$ 5,915
Voting interest acquired (percent)			100.00%
Total Net Assets Acquired			$ 120,708
Loans assumed			$ 314,656
Number of banking, mortgage, and investment offices | branch			48
Intangible assets, including goodwill			$ 186,992
Goodwill resulting from merger	[1]		174,736
Core deposit intangible	[1]		$ 12,256
Number of loss sharing agreements acquired | agreement			2
Heritage Financial Group | Core Deposits
Business Acquisition [Line Items]
Weighted average useful life (in years)			10 years
Heritage Financial Group | Common Stock
Business Acquisition [Line Items]
Shares issued to common shareholders (shares) | shares			8,635,879
First M&F Merger
Business Acquisition [Line Items]
Total Purchase Price				$ 156,845
Voting interest acquired (percent)				100.00%
Intangible assets, including goodwill				$ 115,159
Goodwill resulting from merger				$ 90,127
Number of branches in operation | branch				43
First M&F Merger | Core Deposits
Business Acquisition [Line Items]
Core deposit intangible				$ 25,032
Weighted average useful life (in years)				10 years
First M&F Merger | Junior Subordinated Debt
Business Acquisition [Line Items]
Loans assumed				$ 30,928
Variable interest rate of derivatives, description				90-day LIBOR
Fair value adjustment				$ 12,371
First M&F Merger | LIBOR | Junior Subordinated Debt
Business Acquisition [Line Items]
Basis spread on variable rate (percent)				1.33%
First M&F Merger | Common Stock
Business Acquisition [Line Items]
Shares issued to common shareholders (shares) | shares				6,175,576
Royal Bank Client
Business Acquisition [Line Items]
Assets under management								$ 680,000
Trust transferred under acquisition (trust) | trust								200
American Trust Bank
Business Acquisition [Line Items]
Number of branches in the northwest region of Georgia (branches) | branch									3
Value of loans covered in loss-share agreements with the FDIC									$ 73,657
Eligible losses covered (percent)									80.00%
Eligible recoveries covered (percent)									80.00%
Crescent Bank & Trust Company
Business Acquisition [Line Items]
Number of branches in the northwest region of Georgia (branches) | branch										11
Value of loans covered in loss-share agreements with the FDIC										$ 361,472
Other real estate owned										$ 50,168
Eligible losses covered (percent)										80.00%
Subsequent Event | KeyWorth Bank
Business Acquisition [Line Items]
Total Purchase Price		$ 59,000
Payment to stock option holders		$ 3,594
Voting interest acquired (percent)		100.00%
Total Net Assets Acquired		$ 399,250
Loans assumed		$ 284,400
Number of offices in operation | branch		6
Subsequent Event | KeyWorth Bank | Core Deposits
Business Acquisition [Line Items]
Deposits		$ 347,000
Subsequent Event | KeyWorth Bank | Common Stock
Business Acquisition [Line Items]
Shares issued to common shareholders (shares) | shares		1,680,021

[1] The goodwill resulting from the merger has been assigned to the Community Banks operating segment.