Securities - Continuous Unrealized Losses (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Less than 12 Months
Fair Value	$ 227,455	$ 106,735
Unrealized Loss	(3,684)	(771)
12 Months or More
Fair Value	165,977	134,831
Unrealized Loss	(7,283)	(3,428)
Fair Value	393,432	241,566
Unrealized Loss	(10,967)	(4,199)
U.S. gov’t sponsored entities
Less than 12 Months
Fair Value	63,025	55,696
Unrealized Loss	(736)	(540)
12 Months or More
Fair Value	70,211	34,754
Unrealized Loss	(1,967)	(368)
Fair Value	133,236	90,450
Unrealized Loss	(2,703)	(908)
State & political subdivisions
Less than 12 Months
Fair Value	45,113	15,890
Unrealized Loss	(617)	(69)
12 Months or More
Fair Value	7,907	4,104
Unrealized Loss	(479)	(245)
Fair Value	53,020	19,994
Unrealized Loss	(1,096)	(314)
Residential & multi-family mortgage
Less than 12 Months
Fair Value	106,762	30,144
Unrealized Loss	(2,196)	(153)
12 Months or More
Fair Value	62,880	63,699
Unrealized Loss	(3,213)	(1,729)
Fair Value	169,642	93,843
Unrealized Loss	(5,409)	(1,882)
Corporate notes and bonds
Less than 12 Months
Fair Value	5,229	5,005
Unrealized Loss	(29)	(9)
12 Months or More
Fair Value	4,676	9,042
Unrealized Loss	(324)	(453)
Fair Value	9,905	14,047
Unrealized Loss	(353)	(462)
Pooled SBA
Less than 12 Months
Fair Value	7,326	0
Unrealized Loss	(106)	0
12 Months or More
Fair Value	19,377	22,270
Unrealized Loss	(1,206)	(575)
Fair Value	26,703	22,270
Unrealized Loss	(1,312)	(575)
Other
Less than 12 Months
Fair Value	0	0
Unrealized Loss	0	0
12 Months or More
Fair Value	926	962
Unrealized Loss	(94)	(58)
Fair Value	926	962
Unrealized Loss	$ (94)	$ (58)