Securities - Summary of Gross Unrealized Losses and Fair Value of Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Schedule Of Available For Sale Securities [Line Items]
Total temporarily impaired securities, Available-for-sale securities, Less Than 12 Months, Fair Value		$ 102,112
Total temporarily impaired securities, Available-for-sale securities, Less Than 12 Months, Unrealized Loss		(620)
Total temporarily impaired securities, Available-for-sale securities, 12 Months or More, Fair Value		494
Total temporarily impaired securities, Available-for-sale securities, 12 Months or More, Unrealized Loss		(6)
Total temporarily impaired securities, Available-for-sale securities, Fair Value		102,606
Total temporarily impaired securities, Available-for-sale securities, Unrealized Loss		(626)
Total temporarily impaired securities, Held-to-maturity securities, Less Than 12 Months, Fair Value	$ 15,866	111,824
Total temporarily impaired securities, Held-to-maturity securities, Less Than 12 Months, Unrealized Loss	(61)	(1,149)
Total temporarily impaired securities, Held-to-maturity securities, 12 Months or More, Fair Value	20,315	103,105
Total temporarily impaired securities, Held-to-maturity securities, 12 Months or More, Unrealized Loss	(321)	(2,106)
Total temporarily impaired securities, Held-to-maturity securities, Fair Value	36,181	214,929
Total temporarily impaired securities, Held-to-maturity securities, Unrealized Loss	(382)	(3,255)
U.S. Government-Sponsored Entities [Member]
Schedule Of Available For Sale Securities [Line Items]
Total temporarily impaired securities, Available-for-sale securities, Less Than 12 Months, Fair Value		9,923
Total temporarily impaired securities, Available-for-sale securities, Less Than 12 Months, Unrealized Loss		(77)
Total temporarily impaired securities, Available-for-sale securities, Fair Value		9,923
Total temporarily impaired securities, Available-for-sale securities, Unrealized Loss		(77)
Total temporarily impaired securities, Held-to-maturity securities, Less Than 12 Months, Fair Value		2,643
Total temporarily impaired securities, Held-to-maturity securities, Less Than 12 Months, Unrealized Loss		(26)
Total temporarily impaired securities, Held-to-maturity securities, Fair Value		2,643
Total temporarily impaired securities, Held-to-maturity securities, Unrealized Loss		(26)
Residential Mortgage-Backed Securities (Issued by Government-Sponsored Entities) [Member]
Schedule Of Available For Sale Securities [Line Items]
Total temporarily impaired securities, Available-for-sale securities, Less Than 12 Months, Fair Value		89,235
Total temporarily impaired securities, Available-for-sale securities, Less Than 12 Months, Unrealized Loss		(497)
Total temporarily impaired securities, Available-for-sale securities, Fair Value		89,235
Total temporarily impaired securities, Available-for-sale securities, Unrealized Loss		(497)
Total temporarily impaired securities, Held-to-maturity securities, Less Than 12 Months, Fair Value	6,594	99,181
Total temporarily impaired securities, Held-to-maturity securities, Less Than 12 Months, Unrealized Loss	(4)	(1,077)
Total temporarily impaired securities, Held-to-maturity securities, 12 Months or More, Fair Value	11,513	87,992
Total temporarily impaired securities, Held-to-maturity securities, 12 Months or More, Unrealized Loss	(98)	(1,629)
Total temporarily impaired securities, Held-to-maturity securities, Fair Value	18,107	187,173
Total temporarily impaired securities, Held-to-maturity securities, Unrealized Loss	(102)	(2,706)
Corporate [Member]
Schedule Of Available For Sale Securities [Line Items]
Total temporarily impaired securities, Available-for-sale securities, Less Than 12 Months, Fair Value		2,954
Total temporarily impaired securities, Available-for-sale securities, Less Than 12 Months, Unrealized Loss		(46)
Total temporarily impaired securities, Available-for-sale securities, Fair Value		2,954
Total temporarily impaired securities, Available-for-sale securities, Unrealized Loss		(46)
Total temporarily impaired securities, Held-to-maturity securities, Less Than 12 Months, Fair Value		5,505
Total temporarily impaired securities, Held-to-maturity securities, Less Than 12 Months, Unrealized Loss		(12)
Total temporarily impaired securities, Held-to-maturity securities, 12 Months or More, Fair Value	7,445	7,253
Total temporarily impaired securities, Held-to-maturity securities, 12 Months or More, Unrealized Loss	(221)	(360)
Total temporarily impaired securities, Held-to-maturity securities, Fair Value	7,445	12,758
Total temporarily impaired securities, Held-to-maturity securities, Unrealized Loss	(221)	(372)
Equity Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Total temporarily impaired securities, Available-for-sale securities, 12 Months or More, Fair Value		494
Total temporarily impaired securities, Available-for-sale securities, 12 Months or More, Unrealized Loss		(6)
Total temporarily impaired securities, Available-for-sale securities, Fair Value		494
Total temporarily impaired securities, Available-for-sale securities, Unrealized Loss		(6)
Small Business Administration Loan Pools [Member]
Schedule Of Available For Sale Securities [Line Items]
Total temporarily impaired securities, Held-to-maturity securities, Less Than 12 Months, Fair Value		1,315
Total temporarily impaired securities, Held-to-maturity securities, Less Than 12 Months, Unrealized Loss		(5)
Total temporarily impaired securities, Held-to-maturity securities, 12 Months or More, Fair Value	1,357	1,560
Total temporarily impaired securities, Held-to-maturity securities, 12 Months or More, Unrealized Loss	(2)	(40)
Total temporarily impaired securities, Held-to-maturity securities, Fair Value	1,357	2,875
Total temporarily impaired securities, Held-to-maturity securities, Unrealized Loss	(2)	(45)
State and Political Subdivisions [Member]
Schedule Of Available For Sale Securities [Line Items]
Total temporarily impaired securities, Held-to-maturity securities, Less Than 12 Months, Fair Value	9,272	3,180
Total temporarily impaired securities, Held-to-maturity securities, Less Than 12 Months, Unrealized Loss	(57)	(29)
Total temporarily impaired securities, Held-to-maturity securities, 12 Months or More, Fair Value		6,300
Total temporarily impaired securities, Held-to-maturity securities, 12 Months or More, Unrealized Loss		(77)
Total temporarily impaired securities, Held-to-maturity securities, Fair Value	9,272	9,480
Total temporarily impaired securities, Held-to-maturity securities, Unrealized Loss	$ (57)	$ (106)