Loans and Allowance for Loan Losses - Activity in ALL by Class of Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	$ 51,550	$ 47,921	$ 51,666	$ 48,693
Charge- offs	(672)	(879)	(1,271)	(2,760)
Recoveries	97	122	266	1,159
Net charge- offs	(575)	(757)	(1,005)	(1,601)
Provisions charged to operations	1,225	1,841	1,539	1,913
Balance at end of period	52,200	49,005	52,200	49,005
Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	6,650	5,562	6,195	5,602
Charge- offs		(40)	(19)	(72)
Recoveries		3	1	4
Net charge- offs		(37)	(18)	(68)
Provisions charged to operations	(224)	160	249	151
Balance at end of period	6,426	5,685	6,426	5,685
Real Estate [Member] | Non-residential Real Estate Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	10,548	10,788	10,519	10,793
Charge- offs		(25)	(1)	(26)
Recoveries		1	39	2
Net charge- offs		(24)	38	(24)
Provisions charged to operations	157	(284)	148	(289)
Balance at end of period	10,705	10,480	10,705	10,480
Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	3,281	3,130	3,226	3,129
Charge- offs	(6)	(36)	(62)	(156)
Recoveries	23	10	26	11
Net charge- offs	17	(26)	(36)	(145)
Provisions charged to operations	9	44	117	164
Balance at end of period	3,307	3,148	3,307	3,148
Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	9,831	8,659	9,672	8,622
Charge- offs	(151)	(16)	(241)	(73)
Recoveries	3	6	6	17
Net charge- offs	(148)	(10)	(235)	(56)
Provisions charged to operations	440	263	686	346
Balance at end of period	10,123	8,912	10,123	8,912
Commercial and Financial [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	14,785	12,810	15,334	12,421
Charge- offs	(153)	(471)	(309)	(677)
Recoveries	10	61	23	979
Net charge- offs	(143)	(410)	(286)	302
Provisions charged to operations	427	1,243	21	920
Balance at end of period	15,069	13,643	15,069	13,643
Consumer Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	2,699	2,725	2,793	2,804
Charge- offs	(194)	(234)	(444)	(468)
Recoveries	44	32	124	83
Net charge- offs	(150)	(202)	(320)	(385)
Provisions charged to operations	290	183	366	287
Balance at end of period	2,839	2,706	2,839	2,706
Other Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	2,336	2,958	2,481	4,045
Charge- offs	(2)	(56)	(2)	(1,274)
Recoveries	12	1	24	5
Net charge- offs	10	(55)	22	(1,269)
Provisions charged to operations	(18)	103	(175)	230
Balance at end of period	2,328	3,006	2,328	3,006
Acquired Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	1,420	1,289	1,446	1,277
Charge- offs	(166)	(1)	(193)	(14)
Recoveries	5	8	23	58
Net charge- offs	(161)	7	(170)	44
Provisions charged to operations	144	129	127	104
Balance at end of period	$ 1,403	$ 1,425	$ 1,403	$ 1,425