Summary of Effective Tax Rate (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Effective income tax rate reconciliation
Federal statutory rate	21.00%	21.00%	35.00%
State taxes, net of federal income tax benefit	4.40%	4.80%	4.60%
Tax rate change	0.00%	0.00%	10.90%
Tax-exempt interest income	(3.70%)	(5.00%)	(10.50%)
Tax credits	(4.50%)	(4.20%)	(3.20%)
Other, net	1.60%	1.60%	(1.10%)
Effective income tax rate	18.80%	18.20%	35.70%