Securities - Amortized Cost and Fair Value of Securities Available for Sale and Held to Maturity (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Amortized cost within one year	$ 29,589	$ 20,532
Amortized cost one to five years	52,250	42,476
Amortized cost for five to ten years	100,190	107,839
Amortized cost for after ten years	95,233	67,020
Total amortized cost	277,262	237,867
Total available for sale investment securities, Amortized Cost	684,023	608,909
Within one year, amortized cost	150	70
One to five years, amortized cost	50,317	48,732
Five to ten years, amortized cost	99,413	101,809
After ten years, amortized cost	37,967	40,658
Total amortized cost	187,847	191,269
Total held to maturity investment securities, amortized cost	206,327	210,112
Fair value within one year	29,552	20,448
Fair value for one to five years	51,759	41,705
Fair value for five to ten years	102,334	107,107
Fair value for after ten years	98,189	67,349
Total fair value	281,834	236,609
Investment securities, available for sale	687,142	600,348
Within one year, fair value	150	70
One to five years, fair value	51,152	49,324
five to ten years, fair value	101,178	101,533
After ten years, fair value	37,207	38,749
Total fair value	189,687	189,676
Held-to-maturity, Fair Value	210,106	208,273
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
Total held to maturity investment securities, amortized cost	5,019	5,144
Investment securities, available for sale	213,043	185,003
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
Total held to maturity investment securities, amortized cost	13,461	13,699
Investment securities, available for sale	192,265	178,736
Held-to-maturity, Fair Value	$ 13,557	$ 13,567

Available for sale securities debt maturities rolling fair value.

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Held to maturity securities debt maturities amortized cost.

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Held To Maturity Securities Debt Maturities Fair Value Aggregate

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in next rolling fiscal year following latest fiscal year. For interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing after rolling tenth fiscal year following latest fiscal year. For interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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Fair value of investment in debt security, measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in rolling sixth through tenth fiscal year following latest fiscal year. For interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in next rolling fiscal year through fifth year following latest fiscal year. For interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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Fair value of investment in debt security, measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in next rolling fiscal year through fifth year following latest fiscal year. For interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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Amount of investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562

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-Paragraph 5
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563

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Fair value of investment in debt security measured at amortized cost (held-to-maturity), with single maturity date and allocated without single maturity date, maturing in second through fifth rolling fiscal year following latest fiscal year. For interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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-Name Accounting Standards Codification
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Amount of investment in debt security measured at amortized cost (held-to-maturity), with single maturity date and allocated without single maturity date, maturing after rolling tenth fiscal year following latest fiscal year. For interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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Amount of investment in debt security measured at amortized cost (held-to-maturity), with single maturity date and allocated without single maturity date, maturing in sixth through tenth rolling fiscal year following latest fiscal year. For interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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