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		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Included in net income	$ (112)	$ (324)	$ (324)	$ 145
Hedged Loans [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Included in net income	(4)	(830)	423	2,781
Interest Rate Swap [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Included in net income	4	830	(423)	(2,781)
Derivative Loan Commitments [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Included in net income	$ (112)	$ (324)	$ (324)	$ 145