Commitments and Contingencies - Summary of Off-Balance Sheet Financial Instruments (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financial instruments with contract amounts which represent potential credit risk:
Loan commitments	$ 1,305,003	$ 1,214,553
Commercial mortgage loan commitments
Financial instruments with contract amounts which represent potential credit risk:
Loan commitments	32,346	25,821
Commercial loan commitments
Financial instruments with contract amounts which represent potential credit risk:
Loan commitments	645,924	610,838
Commercial owner-occupied commitments
Financial instruments with contract amounts which represent potential credit risk:
Loan commitments	55,545	55,205
Commercial standby letters of credit
Financial instruments with contract amounts which represent potential credit risk:
Loan commitments	75,446	71,612
Residential mortgage loan commitments
Financial instruments with contract amounts which represent potential credit risk:
Loan commitments	8,057	1,636
Consumer loan commitments
Financial instruments with contract amounts which represent potential credit risk:
Loan commitments	296,010	259,501
Construction loan commitments
Financial instruments with contract amounts which represent potential credit risk:
Loan commitments	$ 191,675	$ 189,940