Loans and Allowance for Loan Losses - Activity in ALL by Class of Loans (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period				$ 41,666				$ 40,889	$ 41,666	$ 40,889
Charge- offs									(4,907)	(7,325)
Recoveries									415	427
Net charge- offs									(4,492)	(6,898)
Provisions charged to operations	$ 1,672	$ 2,940	$ 2,804	4,103	$ 3,646	$ 1,424	$ 1,271	1,334	11,519	7,675	$ 3,072
Balance at end of period	48,693				41,666				48,693	41,666	40,889
Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period				4,661				4,406	4,661	4,406
Charge- offs									(11)	(37)
Recoveries									3	1
Net charge- offs									(8)	(36)
Provisions charged to operations									949	291
Balance at end of period	5,602				4,661				5,602	4,661	4,406
Real Estate [Member] | Non-residential Real Estate Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period				9,921				9,616	9,921	9,616
Charge- offs									(9)	(708)
Recoveries									6	2
Net charge- offs									(3)	(706)
Provisions charged to operations									875	1,011
Balance at end of period	10,793				9,921				10,793	9,921	9,616
Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period				3,148				2,948	3,148	2,948
Charge- offs									(208)	(222)
Recoveries									55	40
Net charge- offs									(153)	(182)
Provisions charged to operations									134	382
Balance at end of period	3,129				3,148				3,129	3,148	2,948
Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period				6,725				6,269	6,725	6,269
Charge- offs									(181)	(138)
Recoveries									21	17
Net charge- offs									(160)	(121)
Provisions charged to operations									2,057	577
Balance at end of period	8,622				6,725				8,622	6,725	6,269
Commercial and Financial [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period				11,754				12,771	11,754	12,771
Charge- offs									(2,921)	(3,799)
Recoveries									122	199
Net charge- offs									(2,799)	(3,600)
Provisions charged to operations									3,466	2,583
Balance at end of period	12,421				11,754				12,421	11,754	12,771
Consumer Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period				2,642				2,404	2,642	2,404
Charge- offs									(1,088)	(626)
Recoveries									159	124
Net charge- offs									(929)	(502)
Provisions charged to operations									1,091	740
Balance at end of period	2,804				2,642				2,804	2,642	2,404
Other Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period				2,648				2,359	2,648	2,359
Charge- offs									(388)	(1,109)
Recoveries									17	16
Net charge- offs									(371)	(1,093)
Provisions charged to operations									1,768	1,382
Balance at end of period	4,045				2,648				4,045	2,648	2,359
Acquired Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period				$ 167				$ 116	167	116
Charge- offs									(101)	(686)
Recoveries									32	28
Net charge- offs									(69)	(658)
Provisions charged to operations									1,179	709
Balance at end of period	$ 1,277				$ 167				$ 1,277	$ 167	$ 116