Employee Benefit Plans (Details 3) - Pension Plan	12 Months Ended
	Dec. 31, 2018
Employee benefits plans
Period of operating history and sufficient trading volume of invested entity (minimum)	5 years
Minimum
Employee benefits plans
Period to meet policy goals	3 years
Maximum
Employee benefits plans
Period to meet policy goals	5 years
Domestic Equities
Employee benefits plans
Target (as a percent)	50.00%
Domestic Equities | Minimum
Employee benefits plans
Target (as a percent)	35.00%
Domestic Equities | Maximum
Employee benefits plans
Target (as a percent)	75.00%
Large Cap Growth
Employee benefits plans
Target (as a percent)	22.50%
Large Cap Growth | Minimum
Employee benefits plans
Target (as a percent)	15.00%
Large Cap Growth | Maximum
Employee benefits plans
Target (as a percent)	30.00%
Large Cap Value
Employee benefits plans
Target (as a percent)	22.50%
Large Cap Value | Minimum
Employee benefits plans
Target (as a percent)	15.00%
Large Cap Value | Maximum
Employee benefits plans
Target (as a percent)	30.00%
Mid Cap Value
Employee benefits plans
Target (as a percent)	5.00%
Mid Cap Value | Minimum
Employee benefits plans
Target (as a percent)	5.00%
Mid Cap Value | Maximum
Employee benefits plans
Target (as a percent)	15.00%
Mid Cap Growth
Employee benefits plans
Target (as a percent)	0.00%
Mid Cap Growth | Minimum
Employee benefits plans
Target (as a percent)	0.00%
Mid Cap Growth | Maximum
Employee benefits plans
Target (as a percent)	10.00%
Domestic Fixed Income
Employee benefits plans
Target (as a percent)	35.00%
Domestic Fixed Income | Minimum
Employee benefits plans
Target (as a percent)	15.00%
Domestic Fixed Income | Maximum
Employee benefits plans
Target (as a percent)	50.00%
International Equities
Employee benefits plans
Target (as a percent)	15.00%
International Equities | Minimum
Employee benefits plans
Target (as a percent)	10.00%
International Equities | Maximum
Employee benefits plans
Target (as a percent)	25.00%