CREDIT QUALITY ASSESSMENT (Additional Information) (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable Troubled Debt Restructurings Specific Allowance	$ 292	$ 563
Other real estate owned	1,410	1,584
Mortgage Loans in Process of Foreclosure, Amount	0
Non-accrual loans	37,323	33,583
Loans and Leases Receivable, Net of Deferred Income, Total	6,569,990	6,571,634
Homogeneous Loan Pools
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Net of Deferred Income, Total	1,931,799	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	1,916,205	1,917,387
WashingtonFirst Bankshares Inc [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	5,400	4,800
WashingtonFirst Bankshares Inc [Member] | Performing Financing Receivable [Member] | Homogeneous Loan Pools
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	1,100	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	2,000	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	17,600	24,300
WashingtonFirst Bankshares Inc [Member] | Substandard | Performing Financing Receivable [Member] | Credit impaired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Net of Deferred Income, Total	9,200	7,200
Restructured Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable Troubled Debt Restructurings Specific Allowance	300	600
Additional Financing Receivable Troubled Debt Restructurings Restructured	$ 1,800	$ 1,600