Mergers and Acquisitions-SBFC - (Details) - USD ($)	Jan. 03, 2017	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 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
Other real estate owned and repossessed assets	550,000
Deferred tax asset.	15,560,000
Other assets	7,063,000
Total assets	1,834,712,000
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Deposit Liabilities [Abstract]
Total deposits	1,520,920,000
Other liabilities (acquired)	25,533,000
Total liabilities	1,656,967,000
Net identifiable assets acquired over (under) liabilities assumed	177,745,000
Goodwill	257,370,000	$ 595,711,000	$ 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	$ 352,431,000	$ 313,773,000	$ 312,034,000
Other borrowings	109,500,000
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
Other real estate owned 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.	$ 434,625,000
Cash paid for stock options outstanding	490,000
Fair value of total consideration transferred	$ 435,115,000
Purchase price per share of the Company's common stock (in dollars per share)	$ 87.30
Adjustment to acquired loans portfolio	$ 30,749
Allowance for loan losses recorded	20,081
Discount on trust preferred securities	2,149,000,000
Federal Home Loan Bank, Advances, Premium	1,029,000,000
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
Other real estate owned 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