Income Taxes - Effective Tax Rate (Details)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Effective tax rate differs from the federal statutory rate
Statutory Federal income tax rate (as a percent)	35.00%	35.00%	35.00%
State income taxes, net of federal tax benefit (as a percent)	6.90%	6.50%	5.30%
Low income housing credits, net of investment losses (as a percent)	(0.00%)	0.80%	0.60%
Increase in cash surrender value of life insurance (as a percent)	(2.20%)	(2.70%)	(3.50%)
Non-taxable interest income (as a percent)	(2.70%)	(3.20%)	(2.90%)
Split dollar term insurance (as a percent)	0.10%	0.10%	0.20%
Other, net (as a percent)	0.90%	(0.50%)	0.30%
Effective tax rate (as a percent)	38.00%	36.00%	35.00%