Mergers and Acquisitions- Park & SBFC - (Details)				1 Months Ended	12 Months Ended
	Nov. 30, 2017 USD ($) $ / shares shares	Jan. 03, 2017 USD ($) $ / shares shares	Aug. 21, 2015 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Deposit Liabilities [Abstract]
Federal funds purchased and securities sold under agreements to repurchase				$ 286,857,000	$ 286,857,000	$ 286,857,000	$ 313,773,000
Goodwill				999,586,000	999,586,000	999,586,000	338,340,000	$ 338,340,000
Additional information
Provisional income tax expense						26,600,000
Proforma amounts
Total revenues (net interest income plus noninterest income), Pro Forma						690,716,000	684,532,000
Net operating income available to the common shareholder, Pro Forma						146,821,000	$ 164,479,000
Bank of America
Business Combination Recognized Identifiable Assets Acquired [Abstract]
Cash and cash equivalents			$ 428,567,000
Loans, net of allowance and mark			3,150,000
Premises and equipment			4,129,000
Intangible assets			6,800,000
Other assets			66,000
Total assets			442,712,000
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Deposit Liabilities [Abstract]
Noninterest-bearing			97,440,000
Interest-bearing			340,849,000
Total deposits			438,289,000
Other liabilities (acquired)			56,000
Total liabilities			438,345,000
Net identifiable assets acquired over (under) liabilities assumed			4,367,000
Goodwill			20,652,000
Net assets acquired over liabilities assumed			25,019,000
Consideration:
Business combination deposit premium paid			25,019,000
Fair value of total consideration transferred			25,019,000
Additional information
Core deposit intangible			$ 6,800,000
Percentage of average daily deposits for thirty day period			5.5
Bank of America | As previously recorded by acquiree
Business Combination Recognized Identifiable Assets Acquired [Abstract]
Cash and cash equivalents			$ 428,567,000
Loans, net of allowance and mark			3,445,000
Premises and equipment			6,267,000
Other assets			66,000
Total assets			438,345,000
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Deposit Liabilities [Abstract]
Noninterest-bearing			97,440,000
Interest-bearing			340,849,000
Total deposits			438,289,000
Other liabilities (acquired)			56,000
Total liabilities			438,345,000
Bank of America | Initial Fair Value Adjustments
Business Combination Recognized Identifiable Assets Acquired [Abstract]
Loans, net of allowance and mark			(295,000)
Premises and equipment			(2,138,000)
Intangible assets			6,800,000
Total assets			4,367,000
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Deposit Liabilities [Abstract]
Net identifiable assets acquired over (under) liabilities assumed			4,367,000
Goodwill			20,652,000
Net assets acquired over liabilities assumed			25,019,000
Additional information
Core deposit intangible			$ 6,800,000
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 acquired in acquisition		450,000		385,000	385,000	$ 385,000
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 (acquired)		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 | shares		4,978,338
Purchase price per share of the Company's common stock (in dollars per share) | $ / shares		$ 87.30
Company common stock issued ($688,566) and cash exchanged for fractional shares ($88)		$ 434,625,000
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
Core deposit intangible		18,120,000
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
Proforma amounts
Total revenues (net interest income plus noninterest income), Pro Forma					67,823,000
Net operating income available to the common shareholder, Pro Forma					$ 25,790,000
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 acquired in acquisition		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 (acquired)		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
Additional information
Core deposit intangible		140,000
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 acquired in acquisition		(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 (acquired)		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
Additional information
Core deposit intangible		17,980,000
Southeastern Bank Financial | Subsequent Fair Value Adjustments
Business Combination Recognized Identifiable Assets Acquired [Abstract]
Premises and equipment		870,000
OREO acquired in acquisition		(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 (acquired)		2,210,000
Total liabilities		2,210,000
Net identifiable assets acquired over (under) liabilities assumed		(925,000)
Goodwill		$ 925,000
Park Sterling Corporation
Business Combination Recognized Identifiable Assets Acquired [Abstract]
Cash and cash equivalents	$ 116,454,000
Investment securities	462,705,000
Loans held for sale	70,886,000
Loans, net of allowance and mark	2,250,734,000
Premises and equipment	56,177,000
Intangible assets	26,175,000
OREO acquired in acquisition	2,120,000
Bank owned life insurance	72,703,000
Deferred tax asset.	29,559,000
Other assets	21,119,000
Total assets	3,108,632,000
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Deposit Liabilities [Abstract]
Noninterest-bearing	561,874,000
Interest-bearing	1,889,502,000
Total deposits	2,451,376,000
Other borrowings	340,938,000
Other liabilities (acquired)	26,310,000
Total liabilities	2,818,624,000
Net identifiable assets acquired over (under) liabilities assumed	290,008,000
Goodwill	402,951,000
Net assets acquired over liabilities assumed	$ 692,959,000
Consideration:
Common stock shares issued | shares	7,480,343
Purchase price per share of the Company's common stock (in dollars per share) | $ / shares	$ 92.05
Company 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	88.00
Cash paid for stock options outstanding	4,305,000
Fair value of total consideration transferred	692,959,000
Additional information
Allowance for loan losses	12,500,000
Fair value mark on loans	$ 21,300,000
Interest rate on core deposit intangibles (in %)	1.66%
Core deposit intangible	$ 26,175,000
Goodwill write-off	73,100,000
Premium for fixed maturity time deposits	2,950,000
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				14,052,000
Net operating income available to the common shareholder, Pro Forma				$ 4,829,000
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 acquired in acquisition	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 (acquired)	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
Additional information
Core deposit intangible	73,090,000
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 acquired in acquisition	(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 (acquired)	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
Additional information
Adjustment to acquired loans portfolio	60,900,000
Core deposit intangible	$ (46,915,000)