Income Taxes - Effective Tax Rate (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Effective tax rate differs from the federal statutory rate
Statutory Federal income tax rate (as a percent)	21.00%	21.00%	35.00%
State income taxes, net of federal tax benefit (as a percent)	8.50%	8.50%	6.80%
Low income housing credits, net of investment losses (as a percent)	(0.50%)	(0.80%)	(0.50%)
Increase in cash surrender value of life insurance (as a percent)	(0.50%)	(0.50%)	(1.20%)
Stock option/restricted stock windfall tax benefit	(0.30%)	(0.90%)	(0.30%)
Non-taxable interest income (as a percent)	(0.80%)	(0.90%)	(1.50%)
Split dollar term insurance (as a percent)	0.10%	0.10%	0.10%
Merger cost	0.50%	0.50%
Due to enactment of Tax Reform			14.10%
Other, net (as a percent)	0.10%	0.40%	0.10%
Effective tax rate (as a percent)	28.10%	27.40%	52.60%