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, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	$ 47,921	$ 44,571	$ 48,693	$ 41,666
Charge- offs	(879)	(929)	(2,760)	(2,209)
Recoveries	122	120	1,159	202
Net charge- offs	(757)	(809)	(1,601)	(2,007)
Provisions charged to operations	1,841	2,804	1,913	6,907
Balance at end of period	49,005	46,566	49,005	46,566
Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	5,562	4,832	5,602	4,661
Charge- offs	(40)	(9)	(72)	(10)
Recoveries	3		4
Net charge- offs	(37)	(9)	(68)	(10)
Provisions charged to operations	160	73	151	245
Balance at end of period	5,685	4,896	5,685	4,896
Real Estate [Member] | Non-residential Real Estate Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	10,788	10,211	10,793	9,921
Charge- offs	(25)	(3)	(26)	(4)
Recoveries	1	1	2	2
Net charge- offs	(24)	(2)	(24)	(2)
Provisions charged to operations	(284)	93	(289)	383
Balance at end of period	10,480	10,302	10,480	10,302
Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	3,130	3,164	3,129	3,148
Charge- offs	(36)	(49)	(156)	(99)
Recoveries	10	21	11	38
Net charge- offs	(26)	(28)	(145)	(61)
Provisions charged to operations	44	67	164	116
Balance at end of period	3,148	3,203	3,148	3,203
Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	8,659	7,989	8,622	6,725
Charge- offs	(16)	(70)	(73)	(137)
Recoveries	6	7	17	11
Net charge- offs	(10)	(63)	(56)	(126)
Provisions charged to operations	263	367	346	1,694
Balance at end of period	8,912	8,293	8,912	8,293
Commercial and Financial [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	12,810	12,813	12,421	11,754
Charge- offs	(471)	(502)	(677)	(1,305)
Recoveries	61	35	979	46
Net charge- offs	(410)	(467)	302	(1,259)
Provisions charged to operations	1,243	1,095	920	2,946
Balance at end of period	13,643	13,441	13,643	13,441
Consumer Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	2,725	2,553	2,804	2,642
Charge- offs	(234)	(134)	(468)	(355)
Recoveries	32	38	83	76
Net charge- offs	(202)	(96)	(385)	(279)
Provisions charged to operations	183	292	287	386
Balance at end of period	2,706	2,749	2,706	2,749
Other Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	2,958	2,790	4,045	2,648
Charge- offs	(56)	(149)	(1,274)	(282)
Recoveries	1	7	5	13
Net charge- offs	(55)	(142)	(1,269)	(269)
Provisions charged to operations	103	729	230	998
Balance at end of period	3,006	3,377	3,006	3,377
Acquired Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period	1,289	219	1,277	167
Charge- offs	(1)	(13)	(14)	(17)
Recoveries	8	11	58	16
Net charge- offs	7	(2)	44	(1)
Provisions charged to operations	129	88	104	139
Balance at end of period	$ 1,425	$ 305	$ 1,425	$ 305