Securities - Summary of Securities with Unrealized Losses, Segregated by Duration of Unrealized Loss (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Available for Sale
Available-for-sale Securities, Less than 12 Months, Fair Value	$ 190,508	$ 189,005
Available-for-sale Securities, Less than 12 Months, Unrealized Losses	1,339	352
Available-for-sale Securities, 12 Months or Longer, Fair Value	25,821	21,163
Available-for-sale Securities, 12 Months or Longer, Unrealized Losses	832	582
Available-for-sale Securities, Fair Value, Total	216,329	210,168
Available-for-sale Securities, Unrealized Losses, Total	2,171	934
Held for Investment
Held-to-maturity Securities, Less than 12 Months, Fair Value	483	21
Held-to-maturity Securities, Less than 12 Months, Unrealized Losses	4
Held-to-maturity Securities, 12 Months or Longer, Fair Value	9
Held-to-maturity Securities, Fair Value, Total	492	21
Held-to-maturity Securities, Unrealized Losses, Total	4
U.S. Treasuries [Member]
Available for Sale
Available-for-sale Securities, Less than 12 Months, Fair Value	103,705	139,762
Available-for-sale Securities, Less than 12 Months, Unrealized Losses	920	45
Available-for-sale Securities, Fair Value, Total	103,705	139,762
Available-for-sale Securities, Unrealized Losses, Total	920	45
U.S. Federal Agencies [Member]
Available for Sale
Available-for-sale Securities, Less than 12 Months, Fair Value	71,511	46,948
Available-for-sale Securities, Less than 12 Months, Unrealized Losses	357	118
Available-for-sale Securities, 12 Months or Longer, Fair Value	9,619	5,969
Available-for-sale Securities, 12 Months or Longer, Unrealized Losses	48	35
Available-for-sale Securities, Fair Value, Total	81,130	52,917
Available-for-sale Securities, Unrealized Losses, Total	405	153
Mortgage Backed Securities [Member]
Available for Sale
Available-for-sale Securities, Less than 12 Months, Fair Value	3	59
Available-for-sale Securities, 12 Months or Longer, Fair Value	14,834	14,844
Available-for-sale Securities, 12 Months or Longer, Unrealized Losses	567	543
Available-for-sale Securities, Fair Value, Total	14,837	14,903
Available-for-sale Securities, Unrealized Losses, Total	567	543
Held for Investment
Held-to-maturity Securities, Less than 12 Months, Fair Value	7	21
Held-to-maturity Securities, 12 Months or Longer, Fair Value	9
Held-to-maturity Securities, Fair Value, Total	16	21
States and Political Subdivisions [Member]
Available for Sale
Available-for-sale Securities, Less than 12 Months, Fair Value	15,289	1,932
Available-for-sale Securities, Less than 12 Months, Unrealized Losses	62	47
Available-for-sale Securities, 12 Months or Longer, Fair Value	779	245
Available-for-sale Securities, 12 Months or Longer, Unrealized Losses	67	1
Available-for-sale Securities, Fair Value, Total	16,068	2,177
Available-for-sale Securities, Unrealized Losses, Total	129	48
Held for Investment
Held-to-maturity Securities, Less than 12 Months, Fair Value	476
Held-to-maturity Securities, Less than 12 Months, Unrealized Losses	4
Held-to-maturity Securities, Fair Value, Total	476
Held-to-maturity Securities, Unrealized Losses, Total	4
Other Securities [Member]
Available for Sale
Available-for-sale Securities, Less than 12 Months, Fair Value		304
Available-for-sale Securities, Less than 12 Months, Unrealized Losses		142
Available-for-sale Securities, 12 Months or Longer, Fair Value	589	105
Available-for-sale Securities, 12 Months or Longer, Unrealized Losses	150	3
Available-for-sale Securities, Fair Value, Total	589	409
Available-for-sale Securities, Unrealized Losses, Total	$ 150	$ 145

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position.

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for less than twelve months.

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