Business Combination - Schedule of Fair Value of Assets Acquired and Liabilities Assumed (Detail) - USD ($) $ in Thousands	Apr. 01, 2017	Sep. 30, 2018	Dec. 31, 2017	[1]
Identifiable liabilities assumed:
Goodwill resulting from acquisition		$ 10,374	$ 10,374
As Recorded by the Company
Consideration paid:
Bay Banks of Virginia, Inc. common stock	$ 42,247
Identifiable assets acquired:
Cash and due from banks	2,356
Interest-bearing deposits	12,342
Securities available-for-sale	22,088
Restricted securities	1,543
Loans receivable	210,411
Loans held for sale	55,648
Deferred income taxes	1,580
Premises and equipment	6,036
Accrued interest receivable	1,229
Other real estate owned	3,113
Core deposit intangible	3,670
Bank owned life insurance	8,430
Mortgage servicing rights	324
Other assets	365
Total identified assets acquired	329,135
Identifiable liabilities assumed:
Noninterest-bearing deposits	21,119
Savings and interest-bearing demand deposits	124,640
Time deposits	122,170
Federal Home Loan Bank advances	25,000
Other liabilities	1,525
Total identifiable liabilities assumed	294,454
Total identifiable assets assumed	34,681
Goodwill resulting from acquisition	7,566
Fair Value Adjustments and Reclassifications
Identifiable assets acquired:
Loans receivable	(62,068)
Loans held for sale	55,648
Deferred income taxes	255
Premises and equipment	2,703
Accrued interest receivable	(24)
Core deposit intangible	3,670
Total identified assets acquired	184
Identifiable liabilities assumed:
Time deposits	733
Total identifiable liabilities assumed	733
Total identifiable assets assumed	(549)
Virginia BanCorp
Identifiable assets acquired:
Cash and due from banks	2,356
Interest-bearing deposits	12,342
Securities available-for-sale	22,088
Restricted securities	1,543
Loans receivable	272,479
Deferred income taxes	1,325
Premises and equipment	3,333
Accrued interest receivable	1,253
Other real estate owned	3,113
Bank owned life insurance	8,430
Mortgage servicing rights	324
Other assets	365
Total identified assets acquired	328,951
Identifiable liabilities assumed:
Noninterest-bearing deposits	21,119
Savings and interest-bearing demand deposits	124,640
Time deposits	121,437
Federal Home Loan Bank advances	25,000
Other liabilities	1,525
Total identifiable liabilities assumed	293,721
Total identifiable assets assumed	35,230
Goodwill resulting from acquisition	$ 7,600

[1] Derived from audited December 31, 2017 Consolidated Financial Statements.