Property, Plant and Equipment - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Amortization expense on assets recorded under capital leases	$ 800	$ 1,500	$ 1,700
Accumulated depreciation and amortization, capital lease assets	284,287	242,623
Related Party
Property, Plant and Equipment [Line Items]
Accumulated depreciation and amortization, capital lease assets	800	3,600
Non-Related Party
Property, Plant and Equipment [Line Items]
Accumulated depreciation and amortization, capital lease assets	$ 8,300	$ 4,700