Securities - Summary of Securities with Unrealized Losses, Segregated by Duration of Unrealized Loss (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2013	Dec. 31, 2014
Held for Investment
Held-to-maturity Securities, Less than 12 Months, Fair Value	$ 1
Held-to-maturity Securities, 12 Months or Longer, Fair Value	1,329
Held-to-maturity Securities, 12 Months or Longer, Unrealized Losses	7
Held-to-maturity Securities, Fair Value, Total	1,330
Held-to-maturity Securities, Unrealized Losses, Total	7
Available for Sale
Available-for-sale Securities, Less than 12 Months, Fair Value	111,957	210,274
Available-for-sale Securities, Less than 12 Months, Unrealized Losses	548	902
Available-for-sale Securities, 12 Months or Longer, Fair Value	150,188	14,956
Available-for-sale Securities, 12 Months or Longer, Unrealized Losses	259	218
Available-for-sale Securities, Fair Value, Total	262,145	225,230
Available-for-sale Securities, Unrealized Losses, Total	807	1,120
Mortgage Backed Securities [Member]
Held for Investment
Held-to-maturity Securities, Less than 12 Months, Fair Value	1
Held-to-maturity Securities, 12 Months or Longer, Fair Value	1
Held-to-maturity Securities, Fair Value, Total	2
Available for Sale
Available-for-sale Securities, Less than 12 Months, Fair Value	66	17,041
Available-for-sale Securities, Less than 12 Months, Unrealized Losses	4	585
Available-for-sale Securities, 12 Months or Longer, Fair Value		26
Available-for-sale Securities, 12 Months or Longer, Unrealized Losses		1
Available-for-sale Securities, Fair Value, Total	66	17,067
Available-for-sale Securities, Unrealized Losses, Total	4	586
States and Political Subdivisions [Member]
Held for Investment
Held-to-maturity Securities, 12 Months or Longer, Fair Value	1,328
Held-to-maturity Securities, 12 Months or Longer, Unrealized Losses	7
Held-to-maturity Securities, Fair Value, Total	1,328
Held-to-maturity Securities, Unrealized Losses, Total	7
Available for Sale
Available-for-sale Securities, Less than 12 Months, Fair Value	2,459	3,093
Available-for-sale Securities, Less than 12 Months, Unrealized Losses	72	26
Available-for-sale Securities, 12 Months or Longer, Fair Value		977
Available-for-sale Securities, 12 Months or Longer, Unrealized Losses		23
Available-for-sale Securities, Fair Value, Total	2,459	4,070
Available-for-sale Securities, Unrealized Losses, Total	72	49
U.S. Treasuries [Member]
Available for Sale
Available-for-sale Securities, Less than 12 Months, Fair Value	29,861	149,589
Available-for-sale Securities, Less than 12 Months, Unrealized Losses	85	178
Available-for-sale Securities, Fair Value, Total	29,861	149,589
Available-for-sale Securities, Unrealized Losses, Total	85	178
U.S. Federal Agencies [Member]
Available for Sale
Available-for-sale Securities, Less than 12 Months, Fair Value	79,411	40,551
Available-for-sale Securities, Less than 12 Months, Unrealized Losses	246	113
Available-for-sale Securities, 12 Months or Longer, Fair Value	150,188	13,653
Available-for-sale Securities, 12 Months or Longer, Unrealized Losses	259	62
Available-for-sale Securities, Fair Value, Total	229,599	54,204
Available-for-sale Securities, Unrealized Losses, Total	505	175
Other Securities [Member]
Available for Sale
Available-for-sale Securities, Less than 12 Months, Fair Value	160
Available-for-sale Securities, Less than 12 Months, Unrealized Losses	141
Available-for-sale Securities, 12 Months or Longer, Fair Value		300
Available-for-sale Securities, 12 Months or Longer, Unrealized Losses		132
Available-for-sale Securities, Fair Value, Total	160	300
Available-for-sale Securities, Unrealized Losses, Total	$ 141	$ 132

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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.

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