Employee Benefit Plans (Details 7)		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Benefits
Used to Determine Benefit Obligations at Measurement Date
Discount rate for net periodic cost	[1]			0.65%
Postretirement Benefits
Used to Determine Benefit Obligations at Measurement Date
Discount rate for benefit obligations	[2]	3.40%	4.00%	4.20%
Discount rate for net periodic cost	[1]	3.70%	4.20%	3.90%
Expected long-term return on plan assets		0.00%	0.00%	0.00%
Rate of compensation increases		0.00%	0.00%	0.00%
Supplemental Employee Retirement Plan
Used to Determine Benefit Obligations at Measurement Date
Discount rate for benefit obligations		2.50%	2.40%	2.60%
Discount rate for net periodic cost		2.40%	2.60%	2.40%

[1] The calculated rate for the unfunded employee retirement plan was 2.40%, 2.60% and 2.40% in 2017, 2016 and 2015, respectively. Since it was terminated in 2015, the defined benefit pension plan did not have a discount rate in 2015, 2016 or 2017.

[2] The calculated rate for the unfunded employee retirement plan was 2.50%, 2.40% and 2.60% in 2017, 2016 and 2015, respectively. Since it was terminated in 2015, the defined benefit pension plan did not have a discount rate in 2015, 2016 or 2017.