Loans and Leases - Certain Information Relating to Commercial Real Estate Loans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Loans and Leases Receivable Disclosure [Line Items]
Commercial construction, acquisition and development loans	$ 1,170,175	$ 597,617
Credit Concentration Risk | Commercial construction loans
Loans and Leases Receivable Disclosure [Line Items]
Percent of total loans and leases	5.60%	4.00%
Loan portfolio diversification risk | Commercial real estate loans | Percent owner-occupied
Loans and Leases Receivable Disclosure [Line Items]
Percent of total loans and leases	35.30%	36.20%
Loan portfolio diversification risk | Commercial real estate loans | Percent non-owner-occupied
Loans and Leases Receivable Disclosure [Line Items]
Percent of total loans and leases	64.70%	63.80%