Securities - Fair Value of Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	$ 684,023	$ 608,909
Gross Unrealized Gains	7,815	2,308
Gross Unrealized Losses	(4,696)	(10,869)
Available-for-sale Securities, Fair Value	687,142	600,348
Held-to-maturity, Amortized Cost	206,327	210,112
Held-to-maturity, Gross Unrealized Gains	4,213	1,853
Held-to-maturity, Gross Unrealized Losses	(434)	(3,692)
Held-to-maturity, Fair Value	210,106	208,273
State and Municipal [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	245,577	210,386
Gross Unrealized Gains	5,266	1,495
Gross Unrealized Losses	(1,083)	(2,578)
Available-for-sale Securities, Fair Value	249,760	209,303
Held-to-maturity, Amortized Cost	187,847	191,269
Held-to-maturity, Gross Unrealized Gains	4,053	1,773
Held-to-maturity, Gross Unrealized Losses	(330)	(3,366)
Held-to-maturity, Fair Value	191,570	189,676
Federal Agency Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	212,829	187,563
Gross Unrealized Gains	1,774	625
Gross Unrealized Losses	(1,560)	(3,185)
Available-for-sale Securities, Fair Value	213,043	185,003
Held-to-maturity, Amortized Cost	5,019	5,144
Held-to-maturity, Gross Unrealized Gains	8	6
Held-to-maturity, Gross Unrealized Losses	(48)	(120)
Held-to-maturity, Fair Value	4,979	5,030
Federal Agency Mortgage-backed Pools [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	193,932	183,479
Gross Unrealized Gains	294	80
Gross Unrealized Losses	(1,961)	(4,823)
Available-for-sale Securities, Fair Value	192,265	178,736
Held-to-maturity, Amortized Cost	13,461	13,699
Held-to-maturity, Gross Unrealized Gains	152	74
Held-to-maturity, Gross Unrealized Losses	(56)	(206)
Held-to-maturity, Fair Value	13,557	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	14,087	16,815
Gross Unrealized Gains		1
Gross Unrealized Losses	(92)	(208)
Available-for-sale Securities, Fair Value	13,995	16,608
Corporate Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	17,598	10,666
Gross Unrealized Gains	481	107
Gross Unrealized Losses		(75)
Available-for-sale Securities, Fair Value	$ 18,079	$ 10,698

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

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