Securities - Fair Value of Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	$ 608,909	$ 513,602
Gross Unrealized Gains	2,308	2,502
Gross Unrealized Losses	(10,869)	(6,439)
Available-for-sale Securities, Fair Value	600,348	509,665
Held-to-maturity, Amortized Cost	210,112	200,448
Held-to-maturity, Gross Unrealized Gains	1,853	3,726
Held-to-maturity, Gross Unrealized Losses	(3,692)	(3,089)
Held-to-maturity, Fair Value	208,273	201,085
State and Municipal [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	210,386	148,045
Gross Unrealized Gains	1,495	2,189
Gross Unrealized Losses	(2,578)	(670)
Available-for-sale Securities, Fair Value	209,303	149,564
Held-to-maturity, Amortized Cost	191,269	179,836
Held-to-maturity, Gross Unrealized Gains	1,773	3,493
Held-to-maturity, Gross Unrealized Losses	(3,366)	(2,932)
Held-to-maturity, Fair Value	189,676	180,397
Federal Agency Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	187,563	132,871
Gross Unrealized Gains	625	45
Gross Unrealized Losses	(3,185)	(2,551)
Available-for-sale Securities, Fair Value	185,003	130,365
Held-to-maturity, Amortized Cost	5,144	5,734
Held-to-maturity, Gross Unrealized Gains	6	17
Held-to-maturity, Gross Unrealized Losses	(120)	(69)
Held-to-maturity, Fair Value	5,030	5,682
Federal Agency Mortgage-backed Pools [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	183,479	211,487
Gross Unrealized Gains	80	155
Gross Unrealized Losses	(4,823)	(2,985)
Available-for-sale Securities, Fair Value	178,736	208,657
Held-to-maturity, Amortized Cost	13,699	14,878
Held-to-maturity, Gross Unrealized Gains	74	216
Held-to-maturity, Gross Unrealized Losses	(206)	(88)
Held-to-maturity, Fair Value	13,567	15,006
U.S. Treasury and Federal Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	16,815	19,277
Gross Unrealized Gains	1
Gross Unrealized Losses	(208)	(225)
Available-for-sale Securities, Fair Value	16,608	19,052
Private Labeled Mortgage-backed Pools [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost		1,650
Gross Unrealized Losses		(8)
Available-for-sale Securities, Fair Value		1,642
Corporate Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	10,666	272
Gross Unrealized Gains	107	113
Gross Unrealized Losses	(75)
Available-for-sale Securities, Fair Value	$ 10,698	$ 385

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

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