Investment Securities - Amount of Securities in Unrealized Loss Position (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 15,036	$ 19,942
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(27)	(264)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	4,987	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(25)	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	20,023	19,942
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	(52)	(264)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than Twelve Months, Fair Value	76,626	196,846
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(471)	(5,148)
Twelve Months or Longer, Fair Value	95,818	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1,057)	0
Total, Fair Value	172,444	196,846
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(1,528)	(5,148)
Corporate Bonds [Member]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	15,036	19,942
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(27)	(264)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	4,987	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(25)	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	20,023	19,942
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	(52)	(264)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than Twelve Months, Fair Value	21,949	26,557
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(328)	(1,528)
Twelve Months or Longer, Fair Value	15,805	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(287)	0
Total, Fair Value	37,754	26,557
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(615)	(1,528)
U.S. Treasuries [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than Twelve Months, Fair Value	0	4,708
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	(258)
Twelve Months or Longer, Fair Value	4,845	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(127)	0
Total, Fair Value	4,845	4,708
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(127)	(258)
U.S. Government Corporations and Agencies [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than Twelve Months, Fair Value	39,607	101,813
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(80)	(1,786)
Twelve Months or Longer, Fair Value	62,140	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(452)	0
Total, Fair Value	101,747	101,813
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(532)	(1,786)
State and Political Subdivisions [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than Twelve Months, Fair Value	10,246	30,233
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(31)	(1,049)
Twelve Months or Longer, Fair Value	9,303	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(106)	0
Total, Fair Value	19,549	30,233
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(137)	(1,049)
Residential Mortgage-Backed Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than Twelve Months, Fair Value	4,824	29,444
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(32)	(274)
Twelve Months or Longer, Fair Value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Total, Fair Value	4,824	29,444
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(32)	(274)
Collateralized Mortgage Obligations [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than Twelve Months, Fair Value	0	4,091
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	(253)
Twelve Months or Longer, Fair Value	3,725	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(85)	0
Total, Fair Value	3,725	4,091
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (85)	$ (253)