Employee Benefit Plans - Expected Benefit Payments (Details) - Post-employment benefits $ in Thousands	Dec. 31, 2017 USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2018	$ 486
2019	491
2020	469
2021	443
2022	418
2023-2027	1,221
Total	3,528
Medicare Part D Subsidy Receipts
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2018	15
2019	13
2020	11
2021	11
2022	9
2023-2027	30
Total	$ 89