Mergers and Acquisitions-SBFC - (Details) - USD ($)		9 Months Ended
	Jan. 03, 2017	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
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	1,049,950,000
Premises and equipment	23,207,000
Bank owned life insurance	44,513,000
Intangible assets	18,120,000
OREO and repossessed assets	385,000
Deferred tax asset.	16,410,000
Other assets	7,063,000
Total assets	1,835,397,000
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Deposit Liabilities [Abstract]
Total deposits	1,520,920,000
Other liabilities (acquired)	27,743,000
Total liabilities	1,659,177,000
Net identifiable assets acquired over (under) liabilities assumed	176,220,000
Goodwill	258,895,000	$ 597,236,000	$ 338,340,000	$ 338,340,000
Net assets acquired over liabilities assumed	435,115,000
Federal funds purchased and securities sold under agreements to repurchase	1,014,000	291,099,000	$ 313,773,000	$ 305,268,000
Other borrowings	109,500,000
Consideration:
Fair value adjustments to employee benefit plans		8,259,000
Adjustment of other miscellaneous liabilities		$ 496,000
Subsequent Fair Value Adjustments
Business Combination Recognized Identifiable Assets Acquired [Abstract]
OREO and repossessed assets	(165,000)
Deferred tax asset.	850,000
Total assets	685,000
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	(1,525,000)
Goodwill	1,525,000
Initial Fair Value Adjustments
Business Combination Recognized Identifiable Assets Acquired [Abstract]
Investment securities	(1,770,000)
Loans	(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 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
Other borrowings	(1,120,000)
Interest-bearing Deposits
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Deposit Liabilities [Abstract]
Total deposits	1,257,953,000
Non interest-bearing deposits
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Deposit Liabilities [Abstract]
Total deposits	$ 262,967,000
SBFC
Consideration:
Common stock shares issued	4,978,338
Company common stock issued and cash exchanged for fractional shares.	$ 434,609,000
Cash paid for stock options outstanding	490,000
Fair value of total consideration transferred	435,115,000
Cash paid for fractional shares	16,000
Company common stock issued ($434,609) and cash exchanged for fractional shares ($16)	$ 434,625,000
Purchase price per share of the Company's common stock (in dollars per share)	$ 87.30
Adjustment to acquired loans portfolio	$ 30,749,000
Allowance for loan losses recorded	20,081,000
Discount on trust preferred securities	2,149,000
Federal Home Loan Bank, Advances, Premium	1,029,000
SBFC | 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	1,060,618,000
Premises and equipment	25,419,000
Bank owned life insurance	44,513,000
Intangible assets	140,000
OREO and repossessed assets	580,000
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]
Total deposits	1,520,920,000
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
Federal funds purchased and securities sold under agreements to repurchase	1,014,000
Other borrowings	110,620,000
SBFC | Interest-bearing Deposits | As previously recorded by acquiree
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Deposit Liabilities [Abstract]
Total deposits	1,257,953,000
SBFC | Non interest-bearing deposits | As previously recorded by acquiree
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Deposit Liabilities [Abstract]
Total deposits	$ 262,967,000