Income Taxes - Deferred Tax Assets/Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Components of Deferred Tax Assets and Liabilities [Abstract]
Excess tax basis over book basis of property, plant, and equipment	$ 7,488	$ 7,488
Marketable securities	667	771
Operating loss carryforwards	34,052	28,530
Capital loss carryforwards	13,276	13,470
Other	2,031	1,848
Total future tax assets	57,514	52,107
Valuation allowance for future tax assets	(56,659)	(51,406)
Total income tax assets	855	701
Other investments	855	701
Total deferred income tax liabilities	$ 855	$ 701