Mergers and Acquisitions- Park & SBFC - (Details) - USD ($)				3 Months Ended		6 Months Ended
	Jan. 03, 2018	Nov. 30, 2017	Jan. 03, 2017	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Deposit Liabilities [Abstract]
Federal funds purchased and securities sold under agreements to repurchase				$ 331,969,000	$ 334,018,000	$ 331,969,000	$ 334,018,000	$ 286,857,000
Goodwill				1,002,722,000	595,817,000	1,002,722,000	595,817,000	$ 999,586,000
Park Sterling Corporation
Business Combination Recognized Identifiable Assets Acquired [Abstract]
Cash and cash equivalents		$ 116,454,000
Investment securities		462,924,000
Loans held for sale		70,882,000
Loans, net of allowance and mark		2,241,603,000
Premises and equipment		55,790,000
Intangible assets		29,496,000		29,500,000		29,500,000
OREO and repossessed assets		2,330,000
Bank owned life insurance		72,703,000
Deferred tax asset.		31,584,000
Other assets		21,119,000
Total assets		3,104,885,000
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Deposit Liabilities [Abstract]
Noninterest-bearing		561,874,000
Interest-bearing		1,888,890,000
Total deposits		2,450,764,000
Other borrowings		340,938,000
Other liabilities		26,310,000
Total liabilities		2,818,012,000
Net identifiable assets acquired over (under) liabilities assumed		286,873,000
Goodwill		406,086,000
Net assets acquired over liabilities assumed		$ 692,959,000
Consideration:
Common stock shares issued		7,480,343
Purchase price per share of the SSB's common stock		$ 92.05
SSB common stock issued ($688,566) and cash exchanged for fractional shares ($88)		$ 688,654,000
Common stock issued		688,566,000
Price per fractional share		88,000
Cash paid for stock options outstanding		4,305,000
Fair value of total consideration transferred		692,959,000
Noncash Merger Related Costs					0		0
Merger-related charges/costs				14,100,000	4,300,000	25,400,000	21,000,000
Provision for Loan and Lease Losses				0		678,000
Additional information
Adjustment to acquired loans portfolio		70,100,000
Allowance for loan losses		12,500,000
Fair value mark on loans		$ 21,300,000
Interest rate on core deposit intangibles (in %)		1.66%
Goodwill write-off		$ 73,100,000
Premium for fixed maturity time deposits		2,300,000
Fair value mark on fixed maturity time deposits		253,000
Fair value adjustment on Trust Preferred Securities		2,400,000
Discount on trust preferred securities		14,000,000
Fair value adjustments to employee benefit plans		1,500,000
Proforma amounts
Total revenues (net interest income plus noninterest income), Pro Forma				29,924,000	172,902,000	66,088,000	337,728,000
Net operating income available to the common shareholder, Pro Forma				$ 15,656,000	$ 46,764,000	35,054,000	$ 88,843,000
Park Sterling Corporation | As previously recorded by acquiree
Business Combination Recognized Identifiable Assets Acquired [Abstract]
Cash and cash equivalents		116,454,000
Investment securities		461,261,000
Loans held for sale		2,200,000
Loans, net of allowance and mark		2,346,612,000
Premises and equipment		61,059,000
Intangible assets		73,090,000
OREO and repossessed assets		2,549,000
Bank owned life insurance		72,703,000
Deferred tax asset.		17,963,000
Other assets		21,595,000
Total assets		3,175,486,000
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Deposit Liabilities [Abstract]
Noninterest-bearing		561,874,000
Interest-bearing		1,886,810,000
Total deposits		2,448,684,000
Other borrowings		329,249,000
Other liabilities		24,179,000
Total liabilities		2,802,112,000
Net identifiable assets acquired over (under) liabilities assumed		373,374,000
Net assets acquired over liabilities assumed		373,374,000
Park Sterling Corporation | Initial Fair Value Adjustments
Business Combination Recognized Identifiable Assets Acquired [Abstract]
Investment securities		1,444,000
Loans held for sale		68,686,000
Loans, net of allowance and mark		(95,878,000)
Premises and equipment		(4,882,000)
Intangible assets		(46,915,000)
OREO and repossessed assets		(429,000)
Deferred tax asset.		11,596,000
Other assets		(476,000)
Total assets		(66,854,000)
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Deposit Liabilities [Abstract]
Interest-bearing		2,692,000
Total deposits		2,692,000
Other borrowings		11,689,000
Other liabilities		2,131,000
Total liabilities		16,512,000
Net identifiable assets acquired over (under) liabilities assumed		(83,366,000)
Goodwill		402,951,000
Net assets acquired over liabilities assumed		319,585,000
Park Sterling Corporation | Subsequent Fair Value Adjustments
Business Combination Recognized Identifiable Assets Acquired [Abstract]
Investment securities		219,000
Loans held for sale		(4,000)
Loans, net of allowance and mark		(9,131,000)
Premises and equipment		(387,000)
Intangible assets		3,321,000
OREO and repossessed assets		210,000
Deferred tax asset.		2,025,000
Total assets		(3,747,000)
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Deposit Liabilities [Abstract]
Interest-bearing		(612,000)
Total deposits		(612,000)
Total liabilities		(612,000)
Net identifiable assets acquired over (under) liabilities assumed		(3,135,000)
Goodwill		$ 3,135,000
Southeastern Bank Financial
Business Combination Recognized Identifiable Assets Acquired [Abstract]
Cash and cash equivalents			$ 72,043,000
Investment securities			590,054,000
Loans held for sale			13,652,000
Loans, net of allowance and mark			1,049,950,000
Premises and equipment			24,077,000
Intangible assets			18,120,000
OREO and repossessed assets			450,000
Bank owned life insurance			44,513,000
Deferred tax asset.			16,075,000
Other assets			7,063,000
Total assets			1,835,997,000
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Deposit Liabilities [Abstract]
Noninterest-bearing			262,967,000
Interest-bearing			1,257,953,000
Total deposits			1,520,920,000
Federal funds purchased and securities sold under agreements to repurchase			1,014,000
Other borrowings			109,500,000
Other liabilities			27,743,000
Total liabilities			1,659,177,000
Net identifiable assets acquired over (under) liabilities assumed			176,820,000
Goodwill			258,295,000
Net assets acquired over liabilities assumed			$ 435,115,000
Consideration:
Common stock shares issued			4,978,338
Purchase price per share of the SSB's common stock			$ 87.30
SSB common stock issued ($688,566) and cash exchanged for fractional shares ($88)			$ 434,625,000
Common stock issued			434,609,000
Price per fractional share			16,000
Cash paid for stock options outstanding			490,000
Fair value of total consideration transferred			435,115,000
Additional information
Adjustment to acquired loans portfolio			30,700,000
Allowance for loan losses			20,100,000
Discount on trust preferred securities	$ 2,100,000
Federal Home Loan Bank, Advances, Premium			1,000,000
Fair value adjustments to employee benefit plans						$ 8,300,000
Adjustment of other miscellaneous liabilities	$ 496,000
Southeastern Bank Financial | As previously recorded by acquiree
Business Combination Recognized Identifiable Assets Acquired [Abstract]
Cash and cash equivalents			72,043,000
Investment securities			591,824,000
Loans held for sale			13,652,000
Loans, net of allowance and mark			1,060,618,000
Premises and equipment			25,419,000
Intangible assets			140,000
OREO and repossessed assets			580,000
Bank owned life insurance			44,513,000
Deferred tax asset.			16,247,000
Other assets			7,545,000
Total assets			1,832,581,000
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Deposit Liabilities [Abstract]
Noninterest-bearing			262,967,000
Interest-bearing			1,257,953,000
Total deposits			1,520,920,000
Federal funds purchased and securities sold under agreements to repurchase			1,014,000
Other borrowings			110,620,000
Other liabilities			19,980,000
Total liabilities			1,652,534,000
Net identifiable assets acquired over (under) liabilities assumed			180,047,000
Net assets acquired over liabilities assumed			180,047,000
Southeastern Bank Financial | Initial Fair Value Adjustments
Business Combination Recognized Identifiable Assets Acquired [Abstract]
Investment securities			(1,770,000)
Loans, net of allowance and mark			(10,668,000)
Premises and equipment			(2,212,000)
Intangible assets			17,980,000
OREO and repossessed assets			(30,000)
Deferred tax asset.			(687,000)
Other assets			(482,000)
Total assets			2,131,000
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Deposit Liabilities [Abstract]
Other borrowings			(1,120,000)
Other liabilities			5,553,000
Total liabilities			4,433,000
Net identifiable assets acquired over (under) liabilities assumed			(2,302,000)
Goodwill			257,370,000
Net assets acquired over liabilities assumed			255,068,000
Southeastern Bank Financial | Subsequent Fair Value Adjustments
Business Combination Recognized Identifiable Assets Acquired [Abstract]
Premises and equipment			870,000
OREO and repossessed assets			(100,000)
Deferred tax asset.			515,000
Total assets			1,285,000
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Deposit Liabilities [Abstract]
Other liabilities			2,210,000
Total liabilities			2,210,000
Net identifiable assets acquired over (under) liabilities assumed			(925,000)
Goodwill			$ 925,000