Securities with Unrealized Losses, Presented by Length of Time Securities Have Been in Continuous Unrealized Loss Position (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Investments, Unrealized Loss Position [Line Items]
Less than 12 Months Fair Value	$ 39,227	$ 40,150
Less than 12 Months Unrealized Loss	(195)	(92)
12 Months or More Fair Value	0	0
12 months or More Unrealized Loss	0	0
Total Fair Value	39,227	40,150
Total Unrealized Loss	(195)	(92)
U.S. Treasury and Agency Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than 12 Months Fair Value	19,862	0
Less than 12 Months Unrealized Loss	(138)	0
12 Months or More Fair Value	0	0
12 months or More Unrealized Loss	0	0
Total Fair Value	19,862	0
Total Unrealized Loss	(138)	0
Corporate Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than 12 Months Fair Value	0	0
Less than 12 Months Unrealized Loss	0	0
12 Months or More Fair Value	0	0
12 months or More Unrealized Loss	0	0
Total Fair Value	0	0
Total Unrealized Loss	0	0
Obligations of State and Political Subdivisions [Member]
Investments, Unrealized Loss Position [Line Items]
Less than 12 Months Fair Value	1,042	203
Less than 12 Months Unrealized Loss	(12)	(2)
12 Months or More Fair Value	0	0
12 months or More Unrealized Loss	0	0
Total Fair Value	1,042	203
Total Unrealized Loss	(12)	(2)
Mortgage-backed Securities - Residential [Member]
Investments, Unrealized Loss Position [Line Items]
Less than 12 Months Fair Value	18,323	39,947
Less than 12 Months Unrealized Loss	(45)	(90)
12 Months or More Fair Value	0	0
12 months or More Unrealized Loss	0	0
Total Fair Value	18,323	39,947
Total Unrealized Loss	(45)	(90)
Equity Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than 12 Months Fair Value	0	0
Less than 12 Months Unrealized Loss	0	0
12 Months or More Fair Value	0	0
12 months or More Unrealized Loss	0	0
Total Fair Value	0	0
Total Unrealized Loss	$ 0	$ 0