Income Taxes - Effective Tax Rate (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Effective tax rate differs from the federal statutory rate
Statutory Federal income tax rate (as a percent)	21.00%	21.00%	21.00%
State income taxes, net of federal tax benefit (as a percent)	8.20%	8.50%	8.50%
Low income housing credits, net of investment losses (as a percent)	(0.50%)	(0.50%)	(0.80%)
Increase in cash surrender value of life insurance (as a percent)	(0.80%)	(0.50%)	(0.50%)
Stock option/restricted stock windfall tax benefit	0.60%	(0.30%)	(0.90%)
Non-taxable interest income (as a percent)	(0.80%)	(0.80%)	(0.90%)
Split dollar term insurance (as a percent)	0.10%	0.10%	0.10%
Merger cost	0.00%	0.50%	0.50%
Other, net (as a percent)	0.30%	0.10%	0.40%
Effective tax rate (as a percent)	28.10%	28.10%	27.40%