Investment Securities - Amount of Securities in Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
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	$ 0	$ 15,036
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	(27)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	4,991	4,987
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(19)	(25)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	4,991	20,023
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	(19)	(52)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than Twelve Months, Fair Value	134,444	76,626
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(2,404)	(471)
Twelve Months or Longer, Fair Value	20,621	95,818
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(279)	(1,057)
Total, Fair Value	155,065	172,444
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(2,683)	(1,528)
U.S. Treasuries [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than Twelve Months, Fair Value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
Twelve Months or Longer, Fair Value	4,896	4,845
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(79)	(127)
Total, Fair Value	4,896	4,845
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(79)	(127)
U.S. Government Corporations and Agencies [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than Twelve Months, Fair Value	45,156	39,607
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(131)	(80)
Twelve Months or Longer, Fair Value	4,974	62,140
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(26)	(452)
Total, Fair Value	50,130	101,747
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(157)	(532)
State and Political Subdivisions [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than Twelve Months, Fair Value	28,564	10,246
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(479)	(31)
Twelve Months or Longer, Fair Value	1,336	9,303
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(14)	(106)
Total, Fair Value	29,900	19,549
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(493)	(137)
Residential Mortgage-Backed Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than Twelve Months, Fair Value	4,809	4,824
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(4)	(32)
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	4,809	4,824
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(4)	(32)
Collateralized Mortgage Obligations [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than Twelve Months, Fair Value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
Twelve Months or Longer, Fair Value	3,410	3,725
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(91)	(85)
Total, Fair Value	3,410	3,725
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(91)	(85)
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	0	15,036
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	(27)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	4,991	4,987
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(19)	(25)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	4,991	20,023
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	(19)	(52)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than Twelve Months, Fair Value	55,913	21,949
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1,787)	(328)
Twelve Months or Longer, Fair Value	6,005	15,805
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(69)	(287)
Total, Fair Value	61,918	37,754
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(1,856)	$ (615)
Equity Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than Twelve Months, Fair Value	2
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(3)
Twelve Months or Longer, Fair Value	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Total, Fair Value	2
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (3)