Loans and Allowance for Loan Losses - Activity in ALL by Class of Loans (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	$ 48,693	$ 41,666
Charge- offs	(1,881)	(1,280)
Recoveries	1,037	82
Net charge- offs	(844)	(1,198)
Provisions charged to operations	72	4,103
Balance at end of period	47,921	44,571
Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	5,602	4,661
Charge- offs	(32)	(1)
Recoveries	1
Net charge- offs	(31)	(1)
Provisions charged to operations	(9)	172
Balance at end of period	5,562	4,832
Real Estate [Member] | Non-residential Real Estate Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	10,793	9,921
Charge- offs	(1)	(1)
Recoveries	1	1
Provisions charged to operations	(5)	290
Balance at end of period	10,788	10,211
Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	3,129	3,148
Charge- offs	(120)	(50)
Recoveries	1	17
Net charge- offs	(119)	(33)
Provisions charged to operations	120	49
Balance at end of period	3,130	3,164
Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	8,622	6,725
Charge- offs	(57)	(67)
Recoveries	11	4
Net charge- offs	(46)	(63)
Provisions charged to operations	83	1,327
Balance at end of period	8,659	7,989
Commercial and Financial [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	12,421	11,754
Charge- offs	(206)	(803)
Recoveries	918	11
Net charge- offs	712	(792)
Provisions charged to operations	(323)	1,851
Balance at end of period	12,810	12,813
Consumer Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	2,804	2,642
Charge- offs	(234)	(221)
Recoveries	51	38
Net charge- offs	(183)	(183)
Provisions charged to operations	104	94
Balance at end of period	2,725	2,553
Other Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	4,045	2,648
Charge- offs	(1,218)	(133)
Recoveries	4	6
Net charge- offs	(1,214)	(127)
Provisions charged to operations	127	269
Balance at end of period	2,958	2,790
Acquired Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	1,277	167
Charge- offs	(13)	(4)
Recoveries	50	5
Net charge- offs	37	1
Provisions charged to operations	(25)	51
Balance at end of period	$ 1,289	$ 219