Securities - Fair Value of Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	$ 753,115	$ 608,909
Gross Unrealized Gains	16,564	2,308
Gross Unrealized Losses	(2,449)	(10,869)
Available-for-sale Securities, Fair Value	767,230	600,348
Held-to-maturity, Amortized Cost	210,306	210,112
Held-to-maturity, Gross Unrealized Gains	7,546	1,853
Held-to-maturity, Gross Unrealized Losses	(134)	(3,692)
Held-to-maturity, Fair Value	217,718	208,273
State and Municipal [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	337,336	210,386
Gross Unrealized Gains	11,374	1,495
Gross Unrealized Losses	(1,609)	(2,578)
Available-for-sale Securities, Fair Value	347,101	209,303
Held-to-maturity, Amortized Cost	192,736	191,269
Held-to-maturity, Gross Unrealized Gains	7,335	1,773
Held-to-maturity, Gross Unrealized Losses	(99)	(3,366)
Held-to-maturity, Fair Value	199,972	189,676
Federal Agency Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	243,366	187,563
Gross Unrealized Gains	3,141	625
Gross Unrealized Losses	(424)	(3,185)
Available-for-sale Securities, Fair Value	246,083	185,003
Held-to-maturity, Amortized Cost	4,714	5,144
Held-to-maturity, Gross Unrealized Gains	11	6
Held-to-maturity, Gross Unrealized Losses	(9)	(120)
Held-to-maturity, Fair Value	4,716	5,030
Federal Agency Mortgage-backed Pools [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	144,880	183,479
Gross Unrealized Gains	1,125	80
Gross Unrealized Losses	(408)	(4,823)
Available-for-sale Securities, Fair Value	145,597	178,736
Held-to-maturity, Amortized Cost	12,856	13,699
Held-to-maturity, Gross Unrealized Gains	200	74
Held-to-maturity, Gross Unrealized Losses	(26)	(206)
Held-to-maturity, Fair Value	13,030	13,567
U.S. Treasury and Federal Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	9,915	16,815
Gross Unrealized Gains	2	1
Gross Unrealized Losses	(8)	(208)
Available-for-sale Securities, Fair Value	9,909	16,608
Corporate Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	17,618	10,666
Gross Unrealized Gains	922	107
Gross Unrealized Losses		(75)
Available-for-sale Securities, Fair Value	$ 18,540	$ 10,698

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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