Securities Available-for-Sale - Fair Value and Age of Gross Unrealized Losses by Investment Category (Detail) $ in Thousands	Dec. 31, 2015 USD ($) security	Dec. 31, 2014 USD ($) security
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Number of Positions | security	23	7
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 213,997	$ 59,329
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Unrealized Losses	$ (1,302)	$ (381)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Number of Positions | security	3	13
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 24,014	$ 103,527
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Unrealized Losses	$ (414)	$ (1,456)
Available-for-sale Securities, Continuous Unrealized Loss Position, Number of Positions | security	26	20
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	$ 238,011	$ 162,856
Available-for-sale Securities, Continuous Unrealized Loss Position, Unrealized Losses, Total	$ (1,716)	$ (1,837)
Obligations of U.S. government corporations and agencies
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Number of Positions | security	10	4
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 88,584	$ 39,745
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Unrealized Losses	$ (379)	$ (207)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Number of Positions | security	2	8
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 14,542	$ 63,149
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Unrealized Losses	$ (188)	$ (871)
Available-for-sale Securities, Continuous Unrealized Loss Position, Number of Positions | security	12	12
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	$ 103,126	$ 102,894
Available-for-sale Securities, Continuous Unrealized Loss Position, Unrealized Losses, Total	$ (567)	$ (1,078)
Collateralized mortgage obligations of U.S. government corporations and agencies
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Number of Positions | security	6	1
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 61,211	$ 9,323
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Unrealized Losses	$ (316)	$ (148)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Number of Positions | security	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 0	$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Unrealized Losses	$ 0	$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Number of Positions | security	6	1
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	$ 61,211	$ 9,323
Available-for-sale Securities, Continuous Unrealized Loss Position, Unrealized Losses, Total	$ (316)	$ (148)
Residential mortgage-backed securities of U.S. government corporations and agencies
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Number of Positions | security	1	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 7,993	$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Unrealized Losses	$ (151)	$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Number of Positions | security	0	1
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 0	$ 8,982
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Unrealized Losses	$ 0	$ (154)
Available-for-sale Securities, Continuous Unrealized Loss Position, Number of Positions | security	1	1
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	$ 7,993	$ 8,982
Available-for-sale Securities, Continuous Unrealized Loss Position, Unrealized Losses, Total	$ (151)	$ (154)
Commercial mortgage-backed securities of U.S. government corporations and agencies
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Number of Positions | security	5	1
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 50,839	$ 9,998
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Unrealized Losses	$ (450)	$ (25)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Number of Positions | security	1	2
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 9,472	$ 20,640
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Unrealized Losses	$ (226)	$ (368)
Available-for-sale Securities, Continuous Unrealized Loss Position, Number of Positions | security	6	3
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	$ 60,311	$ 30,638
Available-for-sale Securities, Continuous Unrealized Loss Position, Unrealized Losses, Total	$ (676)	$ (393)
Obligations of states and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Number of Positions | security	1	1
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 5,370	$ 263
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Unrealized Losses	$ (6)	$ (1)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Number of Positions | security	0	2
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 0	$ 10,756
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Unrealized Losses	$ 0	$ (63)
Available-for-sale Securities, Continuous Unrealized Loss Position, Number of Positions | security	1	3
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	$ 5,370	$ 11,019
Available-for-sale Securities, Continuous Unrealized Loss Position, Unrealized Losses, Total	$ (6)	$ (64)