Income Taxes, Effective Tax Rate Reconciliation (Details)	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Jun. 30, 2017
Income Taxes [Abstract]
Tax based on federal statutory rate	21.00%	28.10%	34.00%
State income taxes, net of federal benefit		0.49%	0.89%
Tax-exempt income		(7.03%)	(8.20%)
Captive insurance premium income		(1.78%)	(2.28%)
Other, net		2.35%	0.55%
Total income tax expense		22.13%	24.96%