Loans and Allowance for Loan Losses - Activity in All by Class of Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	$ 46,566	$ 42,621	$ 41,666	$ 40,889
Charge- offs	(1,560)	(3,174)	(3,769)	(4,202)
Recoveries	115	99	317	254
Net charge- offs	(1,445)	(3,075)	(3,452)	(3,948)
Provisions charged to operations	2,940	1,424	9,847	4,029
Balance at end of period	48,061	40,970	48,061	40,970
Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	4,896	4,503	4,661	4,406
Charge- offs	(1)		(11)	(1)
Recoveries				1
Net charge- offs	(1)		(11)
Provisions charged to operations	214	36	459	133
Balance at end of period	5,109	4,539	5,109	4,539
Real Estate [Member] | Non-residential Real Estate Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	10,302	9,880	9,921	9,616
Charge- offs	(5)	(708)	(9)	(708)
Recoveries	1	1	3	2
Net charge- offs	(4)	(707)	(6)	(706)
Provisions charged to operations	285	814	668	1,077
Balance at end of period	10,583	9,987	10,583	9,987
Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	3,203	3,110	3,148	2,948
Charge- offs	(58)	(28)	(157)	(124)
Recoveries	10	15	48	29
Net charge- offs	(48)	(13)	(109)	(95)
Provisions charged to operations	52	(26)	168	218
Balance at end of period	3,207	3,071	3,207	3,071
Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	8,293	6,485	6,725	6,269
Charge- offs	(10)	(48)	(147)	(123)
Recoveries	8	4	19	13
Net charge- offs	(2)	(44)	(128)	(110)
Provisions charged to operations	212	168	1,906	450
Balance at end of period	8,503	6,609	8,503	6,609
Commercial and Financial [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	13,441	13,713	11,754	12,771
Charge- offs	(1,053)	(2,180)	(2,358)	(2,349)
Recoveries	31	38	77	76
Net charge- offs	(1,022)	(2,142)	(2,281)	(2,273)
Provisions charged to operations	(385)	86	2,561	1,159
Balance at end of period	12,034	11,657	12,034	11,657
Consumer Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	2,749	2,499	2,642	2,404
Charge- offs	(374)	(152)	(729)	(382)
Recoveries	61	35	137	90
Net charge- offs	(313)	(117)	(592)	(292)
Provisions charged to operations	443	160	829	430
Balance at end of period	2,879	2,542	2,879	2,542
Other Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	3,377	2,431	2,648	2,359
Charge- offs	(18)	(20)	(300)	(283)
Recoveries	2	6	15	15
Net charge- offs	(16)	(14)	(285)	(268)
Provisions charged to operations	812	134	1,810	460
Balance at end of period	4,173	2,551	4,173	2,551
Acquired Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	305		167	116
Charge- offs	(41)	(38)	(58)	(232)
Recoveries	2		18	28
Net charge- offs	(39)	(38)	(40)	(204)
Provisions charged to operations	1,307	52	1,446	102
Balance at end of period	$ 1,573	$ 14	$ 1,573	$ 14