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Loans and Allowance for Loan Losses - Activity in All by Class of Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period				$ 39,034				$ 38,725	$ 39,034	$ 38,725
Charge- offs									(2,619)	(1,560)
Recoveries									1,402	611
Net charge- offs									(1,217)	(949)
Provisions charged to operations	1,840us-gaap_ProvisionForLoanAndLeaseLosses	(3,115)us-gaap_ProvisionForLoanAndLeaseLosses	3,129us-gaap_ProvisionForLoanAndLeaseLosses	1,218us-gaap_ProvisionForLoanAndLeaseLosses	454us-gaap_ProvisionForLoanAndLeaseLosses	(12)us-gaap_ProvisionForLoanAndLeaseLosses	516us-gaap_ProvisionForLoanAndLeaseLosses	300us-gaap_ProvisionForLoanAndLeaseLosses	3,072us-gaap_ProvisionForLoanAndLeaseLosses	1,258us-gaap_ProvisionForLoanAndLeaseLosses	3,100us-gaap_ProvisionForLoanAndLeaseLosses
Balance at end of period	40,889				39,034				40,889	39,034	38,725
Non-residential Real Estate Owner Occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period				4,827				5,104	4,827	5,104
Charge- offs									(42)	(3)
Recoveries									102	20
Net charge- offs									60	17
Provisions charged to operations									(481)	(294)
Balance at end of period	4,406				4,827				4,406	4,827
Non-residential Real Estate Other [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period				11,026				9,865	11,026	9,865
Charge- offs									(29)	(19)
Recoveries									49	12
Net charge- offs									20	(7)
Provisions charged to operations									(1,430)	1,168
Balance at end of period	9,616				11,026				9,616	11,026
Residential Real Estate Permanent Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period				2,825				2,781	2,825	2,781
Charge- offs									(207)	(162)
Recoveries									78	32
Net charge- offs									(129)	(130)
Provisions charged to operations									252	174
Balance at end of period	2,948				2,825				2,948	2,825
Residential Real Estate All Other [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period				6,708				7,034	6,708	7,034
Charge- offs									(171)	(209)
Recoveries									32	33
Net charge- offs									(139)	(176)
Provisions charged to operations									(300)	(150)
Balance at end of period	6,269				6,708				6,269	6,708
Non-consumer Non-real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period				8,977				9,385	8,977	9,385
Charge- offs									(564)	(217)
Recoveries									70	175
Net charge- offs									(494)	(42)
Provisions charged to operations									4,288	(366)
Balance at end of period	12,771				8,977				12,771	8,977
Consumer Non-real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period				2,556				2,451	2,556	2,451
Charge- offs									(687)	(597)
Recoveries									203	225
Net charge- offs									(484)	(372)
Provisions charged to operations									332	477
Balance at end of period	2,404				2,556				2,404	2,556
Other Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period				1,991				1,885	1,991	1,885
Charge- offs									(351)	(300)
Recoveries									149	75
Net charge- offs									(202)	(225)
Provisions charged to operations									570	331
Balance at end of period	2,359				1,991				2,359	1,991
Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period				124				220	124	220
Charge- offs									(568)	(53)
Recoveries									719	39
Net charge- offs									151	(14)
Provisions charged to operations									(159)	(82)
Balance at end of period	$ 116				$ 124				$ 116	$ 124