Property, Plant and Equipment - Narrative (Details) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| Property, Plant and Equipment [Line Items] | |||
| Amortization expense on assets recorded under capital leases | $ 1,500 | $ 1,700 | $ 1,700 |
| Accumulated depreciation and amortization, capital lease assets | 242,623 | 231,062 | |
| Related Party | |||
| Property, Plant and Equipment [Line Items] | |||
| Accumulated depreciation and amortization, capital lease assets | 3,600 | 9,000 | |
| Non-Related Party | |||
| Property, Plant and Equipment [Line Items] | |||
| Accumulated depreciation and amortization, capital lease assets | $ 4,700 | $ 6,900 | |