Fair Value Measurements (Narrative) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Percentage of securities using market-based information	97.00%
Percentage of securities using model-based techniques	3.00%
Change in discount rate	1.00%
One percent change in affecting fair value of debt obligation, amount	$ 3,000
One percent change in affecting fair value of debt obligation, percent	4.00%
Minimum corporation reserves for commercial loan	500
Change in unrealized gains or losses included in earnings relating to assets still held	0	0
Impaired loans, carrying amount	13,883
Allocated allowance for loan losses	3,252
Fair value of allocated allowance	12,109
Estimated costs to sell	1,478
Provision for fair value measurements included in allowance for loan losses	526
Carrying amount of OREO	3,336
Written down of OREO	2,702
Fair value of OREO	3,017
Estimated cost to sell OREO	315
Loss from OREO included in earnings	$ 634
Short-term borrowings approximate fair value for amounts that mature, days, less than	90 days
Minimum [Member]
Valuation of investment securities basis spread on index	15.00%
Maximum [Member]
Valuation of investment securities basis spread on index	20.00%