Income Taxes (Details) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Effective tax rate (in hundredths)	21.30%	28.10%	20.20%	26.50%
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent	35.00%	21.00%	21.00%	35.00%	35.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Domestic, Amount			$ 1,300,000
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent			0.20%
Minimum [Member]
Significant change in unrecognized tax benefits is reasonably possible, estimated range of change, lower bound	$ 0		$ 0
Maximum [Member]
Significant change in unrecognized tax benefits is reasonably possible, estimated range of change, lower bound	$ 9,700,000		$ 9,700,000