Income Taxes - Income Tax Provision Differences from the Expected Statutory Provision (Details 1)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income tax provision differences from the expected statutory provision
Expected provision at statutory rate	35.00%	35.00%	35.00%
Difference resulting from:
Tax exempt interest income	(12.10%)	(14.00%)	(16.00%)
Increase in value of bank owned life insurance assets	(3.50%)	(2.40%)	(2.30%)
Other, including state income taxes, valuation allowance and rate differential	1.60%	1.60%	0.50%
Provision of income taxes	21.00%	20.20%	17.20%