Summary of Effective Tax Rate (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Effective income tax rate reconciliation
Federal statutory rate	21.00%	35.00%	35.00%
State taxes, net of federal income tax benefit	4.80%	4.60%	3.80%
Tax rate change	0.00%	10.90%	0.00%
Tax-exempt interest income	(5.00%)	(10.50%)	(12.20%)
Tax credits	(4.20%)	(3.20%)	(2.10%)
Other, net	1.60%	(1.10%)	0.20%
Effective tax rate	18.20%	35.70%	24.70%