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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	$ 52,915	$ 51,550	$ 51,389	$ 51,666
Charge- offs	(585)	(672)	(928)	(1,271)
Recoveries	345	97	530	266
Net charge- offs	(240)	(575)	(398)	(1,005)
Provisions charged to operations	2,433	1,225	4,117	1,539
Balance at end of period	55,108	52,200	55,108	52,200
Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	6,655	6,650	6,328	6,195
Charge- offs	(3)		(9)	(19)
Recoveries			1	1
Net charge- offs	(3)		(8)	(18)
Provisions charged to operations	235	(224)	567	249
Balance at end of period	6,887	6,426	6,887	6,426
Real Estate [Member] | Non-residential Real Estate Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	11,362	10,548	11,027	10,519
Charge- offs	(16)		(22)	(1)
Recoveries	1		1	39
Net charge- offs	(15)		(21)	38
Provisions charged to operations	(60)	157	281	148
Balance at end of period	11,287	10,705	11,287	10,705
Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	3,261	3,281	3,261	3,226
Charge- offs	(4)	(6)	(67)	(62)
Recoveries	4	23	9	26
Net charge- offs		17	(58)	(36)
Provisions charged to operations	64	9	122	117
Balance at end of period	3,325	3,307	3,325	3,307
Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	11,046	9,831	10,673	9,672
Charge- offs	(143)	(151)	(195)	(241)
Recoveries	25	3	27	6
Net charge- offs	(118)	(148)	(168)	(235)
Provisions charged to operations	793	440	1,216	686
Balance at end of period	11,721	10,123	11,721	10,123
Commercial and Financial [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	14,409	14,785	13,151	15,334
Charge- offs	(87)	(153)	(157)	(309)
Recoveries	85	10	152	23
Net charge- offs	(2)	(143)	(5)	(286)
Provisions charged to operations	825	427	2,086	21
Balance at end of period	15,232	15,069	15,232	15,069
Consumer Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	3,072	2,699	3,065	2,793
Charge- offs	(162)	(194)	(282)	(444)
Recoveries	38	44	109	124
Net charge- offs	(124)	(150)	(173)	(320)
Provisions charged to operations	286	290	342	366
Balance at end of period	3,234	2,839	3,234	2,839
Other Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	2,408	2,336	2,423	2,481
Charge- offs		(2)		(2)
Recoveries	43	12	78	24
Net charge- offs	43	10	78	22
Provisions charged to operations	(2)	(18)	(52)	(175)
Balance at end of period	2,449	2,328	2,449	2,328
Acquired Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	702	1,420	1,461	1,446
Charge- offs	(170)	(166)	(196)	(193)
Recoveries	149	5	153	23
Net charge- offs	(21)	(161)	(43)	(170)
Provisions charged to operations	292	144	(445)	127
Balance at end of period	$ 973	$ 1,403	$ 973	$ 1,403