Allowance for Loan Losses - Impaired Financing Receivables (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	$ 12,012		$ 12,012		$ 13,066
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	17,175		17,175		19,208
Impaired financing receivables, with no related allowance recorded, Related Allowance
Impaired financing receivables, with an allowance recorded, Recorded Investment	11,758		11,758		13,024
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance	12,444		12,444		14,227
Impaired financing receivables, with an allowance recorded, Related Allowance	3,324		3,324		4,006
Impaired financing receivables, Recorded Investment, Total	23,770		23,770		26,090
Impaired financing receivables, Unpaid Principal Balance, Total	29,619		29,619		33,435
Impaired financing receivables, Related Allowance, Total	3,324		3,324		4,006
Impaired financing receivables, Average Recorded Investment, Total	24,165	25,229	24,807	25,644
Impaired financing receivables, Interest Income Recognized, Total	399	702	820	1,130
Commercial & Agriculture [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	1,472		1,472		5,053
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	1,608		1,608		5,226
Impaired financing receivables, with no related allowance recorded, Related Allowance
Impaired financing receivables, with an allowance recorded, Recorded Investment	3,484		3,484		367
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance	3,588		3,588		385
Impaired financing receivables, with an allowance recorded, Related Allowance	1,384		1,384		286
Impaired financing receivables, Recorded Investment, Total	4,956		4,956		5,420
Impaired financing receivables, Unpaid Principal Balance, Total	5,196		5,196		5,611
Impaired financing receivables, Related Allowance, Total	1,384		1,384		286
Impaired financing receivables, Average Recorded Investment, Total	5,125	4,610	5,178	4,372
Impaired financing receivables, Interest Income Recognized, Total	63	90	131	180
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	7,254		7,254		5,446
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	9,490		9,490		8,114
Impaired financing receivables, with no related allowance recorded, Related Allowance
Impaired financing receivables, with an allowance recorded, Recorded Investment	5,334		5,334		8,495
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance	5,750		5,750		8,681
Impaired financing receivables, with an allowance recorded, Related Allowance	1,081		1,081		2,354
Impaired financing receivables, Recorded Investment, Total	12,588		12,588		13,941
Impaired financing receivables, Unpaid Principal Balance, Total	15,240		15,240		16,795
Impaired financing receivables, Related Allowance, Total	1,081		1,081		2,354
Impaired financing receivables, Average Recorded Investment, Total	12,855	16,471	13,292	16,832
Impaired financing receivables, Interest Income Recognized, Total	204	444	409	703
Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment	3,286		3,286		2,566
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance	6,077		6,077		5,346
Impaired financing receivables, with no related allowance recorded, Related Allowance
Impaired financing receivables, with an allowance recorded, Recorded Investment	2,438		2,438		3,561
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance	2,587		2,587		4,554
Impaired financing receivables, with an allowance recorded, Related Allowance	800		800		1,199
Impaired financing receivables, Recorded Investment, Total	5,724		5,724		6,127
Impaired financing receivables, Unpaid Principal Balance, Total	8,664		8,664		9,900
Impaired financing receivables, Related Allowance, Total	800		800		1,199
Impaired financing receivables, Average Recorded Investment, Total	5,671	4,092	5,794	4,010
Impaired financing receivables, Interest Income Recognized, Total	126	167	269	245
Real Estate Construction [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance					521
Impaired financing receivables, with no related allowance recorded, Related Allowance
Impaired financing receivables, with an allowance recorded, Recorded Investment	480		480		541
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance	497		497		547
Impaired financing receivables, with an allowance recorded, Related Allowance	58		58		107
Impaired financing receivables, Recorded Investment, Total	480		480		541
Impaired financing receivables, Unpaid Principal Balance, Total	497		497		1,068
Impaired financing receivables, Related Allowance, Total	58		58		107
Impaired financing receivables, Average Recorded Investment, Total	483	33	503	414
Impaired financing receivables, Interest Income Recognized, Total	6	1	11	2
Consumer and Other [Member]
Financing Receivable, Impaired [Line Items]
Impaired financing receivables, with no related allowance recorded, Recorded Investment					1
Impaired financing receivables, with no related allowance recorded, Unpaid Principal Balance					1
Impaired financing receivables, with no related allowance recorded, Related Allowance
Impaired financing receivables, with an allowance recorded, Recorded Investment	22		22		60
Impaired financing receivables, with an allowance recorded, Unpaid Principal Balance	22		22		60
Impaired financing receivables, with an allowance recorded, Related Allowance	1		1		60
Impaired financing receivables, Recorded Investment, Total	22		22		61
Impaired financing receivables, Unpaid Principal Balance, Total	22		22		61
Impaired financing receivables, Related Allowance, Total	1		1		60
Impaired financing receivables, Average Recorded Investment, Total	$ 31	$ 23	$ 40	$ 16