CREDIT QUALITY ASSESSMENT (Additional Information) (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable Troubled Debt Restructurings Specific Allowance	$ 457	$ 563
Other real estate owned	1,482	1,584
Non-accrual loans	36,621	33,583
Loans and Leases Receivable, Net of Deferred Income, Total	6,596,548	6,571,634
Homogeneous Loan Pools
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Net of Deferred Income, Total	1,830,497	1,932,871
Performing Financing Receivable [Member] | Homogeneous Loan Pools
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Net of Deferred Income, Total	1,812,275	1,917,387
WashingtonFirst Bankshares Inc [Member] | Performing Financing Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	2,900	4,800
WashingtonFirst Bankshares Inc [Member] | Performing Financing Receivable [Member] | Homogeneous Loan Pools
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	1,200	1,300
WashingtonFirst Bankshares Inc [Member] | Special Mention [Member] | Performing Financing Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Net of Deferred Income, Total	1,000	4,200
WashingtonFirst Bankshares Inc [Member] | Substandard | Credit impaired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Net of Deferred Income, Total	11,900	24,300
WashingtonFirst Bankshares Inc [Member] | Substandard | Performing Financing Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Net of Deferred Income, Total	6,700	7,200
Restructured Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable Troubled Debt Restructurings Specific Allowance	500	600
Other real estate owned	1,500	1,600
Additional Financing Receivable Troubled Debt Restructurings Restructured	$ 2,000	$ 1,600