Annual report pursuant to Section 13 and 15(d)

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Narrative) (Details)

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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Narrative) (Details)
 3 Months Ended 12 Months Ended
Apr. 30, 2018
USD ($)
Dec. 31, 2005
acquisition
Jun. 30, 2018
USD ($)
Dec. 31, 2018
USD ($)
ATM
branch
shares
Dec. 31, 2017
USD ($)
shares
May 01, 2018
USD ($)
Accounting Policies [Line Items]            
Number of bank branches | branch       140    
Number of ATM's | ATM       188    
Number of business acquisitions | acquisition   2        
Federal Home Loan Bank requires Bank to maintain percentage of stock equal to outstanding borrowings       4.25% 4.25%  
Percentage of Federal Reserve Bank of Richmond reserve       6.00% 6.00%  
Number of days past due to charge off real estate secured loans       180 days    
Future payments, contractual term       6 months    
Goodwill       $ 727,168,000 $ 298,528,000  
Impairment charges for goodwill or intangible assets $ 0     0    
Liabilities for post retirement benefits payable to other beneficiaries       10,500,000 6,300,000  
Affordable housing projects, recognized amortization       922,000 1,300,000  
Affordable housing projects, tax credits       1,100,000 858,000  
Affordable housing projects, investment amount       10,800,000 11,000,000  
Affordable housing projects, liability       $ 9,900,000 $ 7,300,000  
Stock options granted | shares       0 0  
Accruals for uncertain tax positions       $ 0 $ 0  
Accumulated other comprehensive income (loss)       (10,273,000) (884,000)  
Retained earnings       $ 467,345,000 $ 379,468,000  
Minimum            
Accounting Policies [Line Items]            
Commercial loans on nonaccrual status, period       90 days    
Period of independent appraisal or valuation       12 months    
Period past due to change TDR status       30 days    
Estimated useful life of bank premises       3 years    
Percentage of fair value of the derivative instruments for the hedge to be highly effective       80.00%    
Interest rate lock commitments period       30 days    
Tax position benefit recognition threshold       50.00%    
Maximum            
Accounting Policies [Line Items]            
Period past due to charge off consumer loans non-real estate secured       120 days    
Estimated useful life of bank premises       50 years    
Percentage of fair value of the derivative instruments for the hedge to be highly effective       125.00%    
Interest rate lock commitments period       120 days    
Xenith            
Accounting Policies [Line Items]            
Number of branches | branch       7    
Accounting Standards Update 2017-12            
Accounting Policies [Line Items]            
Available for sale debt securities, transfer, amount     $ 187,400,000 $ 187,400,000    
Cumulative effects from adoption of new accounting standards           $ 400,000
Accounting Standards Update 2018-02            
Accounting Policies [Line Items]            
Accumulated other comprehensive income (loss)           $ (107,000)
Accounting Standards Update 2017-12 & 2018-02            
Accounting Policies [Line Items]            
Retained earnings       293,000    
Accounting Standards Update 2016-02            
Accounting Policies [Line Items]            
Operating lease, right-of-use asset       51,500,000    
Operating lease, liability       51,500,000    
Interest Rate Lock Commitments            
Accounting Policies [Line Items]            
Derivative, amount       $ 0