Troubled Debts Restructured (Detail) (Troubled debts restructured, USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013 Investment	Mar. 31, 2012 Investment
Commercial | Real estate
Financing Receivable, Modifications [Line Items]
No. of Loans	1	1
Pre-Modification Outstanding Recorded Balance	$ 50	$ 403
Post-Modification Outstanding Recorded Balance	50	403
Commercial | Other
Financing Receivable, Modifications [Line Items]
No. of Loans	2	1
Pre-Modification Outstanding Recorded Balance	1,009	97
Post-Modification Outstanding Recorded Balance	723	97
Residential Mortgage
Financing Receivable, Modifications [Line Items]
No. of Loans	11	9
Pre-Modification Outstanding Recorded Balance	750	839
Post-Modification Outstanding Recorded Balance	1,056	863
Consumer loans | Real estate
Financing Receivable, Modifications [Line Items]
No. of Loans	4	7
Pre-Modification Outstanding Recorded Balance	220	325
Post-Modification Outstanding Recorded Balance	229	326
Consumer loans | Other
Financing Receivable, Modifications [Line Items]
No. of Loans	1
Pre-Modification Outstanding Recorded Balance	11
Post-Modification Outstanding Recorded Balance	11
Consumer loans | Auto
Financing Receivable, Modifications [Line Items]
No. of Loans	2
Pre-Modification Outstanding Recorded Balance	22
Post-Modification Outstanding Recorded Balance	22
Consumer loans | Boat/RV
Financing Receivable, Modifications [Line Items]
No. of Loans	1	1
Pre-Modification Outstanding Recorded Balance	30	10
Post-Modification Outstanding Recorded Balance	$ 30	$ 10