Financial Instruments with Off-Balance-Sheet Risk and Concentrations of Credit Risk - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Schedule Of Financial Instruments With Off Balance Sheet Credit Risk [Line Items]
Commitments to lend additional funds to borrowers	$ 808	$ 20
Standby letters of credit	$ 21,600
Expiry of letters of credit	2024
Loan and lease commitments	$ 973,700
Loan and lease commitments maturing within one year	667,900
Maturing after one year but within three years	135,500
Maturing after three years but within five years	19,100
Maturing after five years	151,200
Letters of credit maturing after one year but within three years	444
Standby letters of credit maturing within one year	21,100
Letters of credit maturing after three year but within five years	0
Letters of credit maturing after five years	80
Maximum
Schedule Of Financial Instruments With Off Balance Sheet Credit Risk [Line Items]
Standby letters of credit	$ 21,600