Disclosures about Fair Value of Assets and Liabilities - Realized Gains and Losses included in Net Income for Periods in Consolidated Statements of Income (Detail) - Non Interest Income Total Gains and Losses [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Included in net income	$ 257	$ 112
Hedged Loans [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Included in net income	(4,051)	2,768
Interest Rate Swap [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Included in net income	4,051	(2,768)
Derivative Loan Commitments [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Included in net income	$ 257	$ 112