Loans and Allowance for Loan Losses - Activity in ALL by Class of Loans (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	$ 51,389	$ 51,666
Charge- offs	(343)	(599)
Recoveries	185	169
Net charge- offs	(158)	(430)
Provisions charged to operations	1,684	314
Balance at end of period	52,915	51,550
Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	6,328	6,195
Charge- offs	(6)	(19)
Recoveries	1	1
Net charge- offs	(5)	(18)
Provisions charged to operations	332	473
Balance at end of period	6,655	6,650
Real Estate [Member] | Non-residential Real Estate Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	11,027	10,519
Charge- offs	(6)	(1)
Recoveries		39
Net charge- offs	(6)	38
Provisions charged to operations	341	(9)
Balance at end of period	11,362	10,548
Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	3,261	3,226
Charge- offs	(63)	(56)
Recoveries	5	3
Net charge- offs	(58)	(53)
Provisions charged to operations	58	108
Balance at end of period	3,261	3,281
Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	10,673	9,672
Charge- offs	(52)	(90)
Recoveries	2	3
Net charge- offs	(50)	(87)
Provisions charged to operations	423	246
Balance at end of period	11,046	9,831
Commercial and Financial [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	13,151	15,334
Charge- offs	(70)	(156)
Recoveries	67	13
Net charge- offs	(3)	(143)
Provisions charged to operations	1,261	(406)
Balance at end of period	14,409	14,785
Consumer Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	3,065	2,793
Charge- offs	(120)	(250)
Recoveries	71	80
Net charge- offs	(49)	(170)
Provisions charged to operations	56	76
Balance at end of period	3,072	2,699
Other Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	2,423	2,481
Recoveries	35	12
Net charge- offs	35	12
Provisions charged to operations	(50)	(157)
Balance at end of period	2,408	2,336
Acquired Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	1,461	1,446
Charge- offs	(26)	(27)
Recoveries	4	18
Net charge- offs	(22)	(9)
Provisions charged to operations	(737)	(17)
Balance at end of period	$ 702	$ 1,420