Fair Value Disclosures - Additional Information (Detail) (USD $)	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Fair Value Disclosures [Line Items]
Loans held for sale, carrying amount	$ 3,600,000
Negative valuation allowance	79,000
Valuation adjustments for loans held for sale		0
Carrying amount of impaired loans	38,600,000	45,200,000
Valuation allowance of impaired loans	230,000	208,000
Mortgage servicing rights valuation allowance	249,000	497,000
Mortgage servicing rights carrying amount	5,500,000	4,600,000
Fair Value, Measurements, Recurring [Member]
Fair Value Disclosures [Line Items]
Assets measured at fair value on a recurring basis	416,807,000	431,281,000
Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Disclosures [Line Items]
Assets measured at fair value on a recurring basis	0	0
Javers Group [Member]
Fair Value Disclosures [Line Items]
Reduction of other noninterest expense	959,000
Fair value of contingent consideration liability	0
Original potential cash payments from contingent consideration, minimum	0
Original potential cash payments from contingent consideration, maximum	1,700,000
Potential cash payments from contingent consideration, period of measurement (in years)	3 years
Potential cash payments from contingent consideration, end date	Jun. 30, 2015
John T. Fretz Insurance Agency, Inc. [Member]
Fair Value Disclosures [Line Items]
Potential cash payments from contingent consideration, period of measurement (in years)	3 years
Potential cash payments from contingent consideration, end date	Apr. 30, 2016
Potential cash payments from contingent consideration, minimum	0
Potential cash payments from contingent consideration, maximum	$ 930,000