Loans - Activity in Allowance for Loan Losses by Portfolio Segment (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 23,451	$ 21,247	$ 16,553
Provision for loan losses	32,047	2,254	4,313
Loans charged-off	(10,457)	(121)	(360)
Recoveries	395	71	741
Total ending allowance balance	45,436	23,451	21,247
Construction and Land Development
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	4,743	3,802	3,776
Provision for loan losses	172	978	(642)
Loans charged-off	(68)	(38)	0
Recoveries	0	1	668
Total ending allowance balance	4,847	4,743	3,802
Commercial Real Estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	6,725	5,981	4,266
Provision for loan losses	1,388	744	1,715
Loans charged-off		0	0
Recoveries		0	0
Total ending allowance balance	8,113	6,725	5,981
Residential Real Estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	4,743	3,834	2,398
Provision for loan losses	(281)	872	1,387
Loans charged-off	(15)	(7)	(1)
Recoveries	15	44	50
Total ending allowance balance	4,462	4,743	3,834
Commercial and Industrial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	7,166	7,587	6,068
Provision for loan losses	30,732	(383)	1,823
Loans charged-off	(10,227)	(49)	(310)
Recoveries	286	11	6
Total ending allowance balance	27,957	7,166	7,587
Consumer and Other
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	74	43	45
Provision for loan losses	36	43	30
Loans charged-off	(147)	(27)	(49)
Recoveries	94	15	17
Total ending allowance balance	$ 57	$ 74	$ 43