Securities - Schedule of Gross Realized Gains and Losses on the Sales and Calls of Securities as well as Gains and Losses on Equity Securities as well as Result of the Adoption of the ASU 2016-01 (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Available-for-Sale Securities, Gross Unrealized Gain (Loss) [Line Items]
Net securities gains	$ 2,909	$ 358	$ 3,566	$ 319
Debt Securities [Member]
Available-for-Sale Securities, Gross Unrealized Gain (Loss) [Line Items]
Gross realized gains	106	5	348	12
Gross realized losses	(18)		(209)	(18)
Net gains (losses) on debt securities	88	5	139	(6)
Equity Securities [Member]
Available-for-Sale Securities, Gross Unrealized Gain (Loss) [Line Items]
Net unrealized gains recognized on securities still held	265	347	868	319
Net realized gains recognized on securities sold	2,556	6	2,559	6
Net gains on equity securities	$ 2,821	$ 353	$ 3,427	$ 325