Fair Value Measurements (Assets and Liabilities Measured on Nonrecurring Basis) (Details) - Trade - Fair Value, Measurements, Recurring - Level 3 $ in Thousands	Dec. 31, 2019 USD ($)
Implied based on market prices | Real propert
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset fair value	$ 608
Valuation Technique, Discounted Cash Flow [Member] | Equity method investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset fair value	12,424
Valuation, Income Approach [Member] | Frac sand assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset fair value	$ 16,546