Variable Interest Entity - Summary of Carrying Amounts of Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Noncontrolling Interest [Line Items]
Cash and cash equivalents	$ 37,161		$ 85,891
Other current assets	27,691		29,980
Property, plant, and equipment, net	937,301		941,476
Intangible assets	353,749		362,038
Long-term operating lease assets, net	64,309	$ 70,900
Other long-term assets	27,944		29,074
Total assets	2,956,938		2,894,704
Current portion of long-term debt	120,255		45,321
Current liabilities	426,356		349,087
Long-term debt	1,411,252		1,487,298
Long-term operating lease liabilities	49,907
Total liabilities	2,194,884		2,147,105
KFPC
Noncontrolling Interest [Line Items]
Cash and cash equivalents	5,007		6,640
Other current assets	19,896		18,363
Property, plant, and equipment, net	157,697		159,893
Intangible assets	8,397		8,590
Long-term operating lease assets, net	6,509
Other long-term assets	10,096		11,838
Total assets	207,602		205,324
Current portion of long-term debt	120,013		45,152
Current liabilities	14,488		14,996
Long-term debt	0		80,255
Long-term operating lease liabilities	6,509
Total liabilities	$ 141,010		$ 140,403