Fair Value Measurements (Summarized Information About Level 3 Fair Value Measurements) (Details) - Level 3 - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Convertible Preferred Securities
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Assets, fair value measurement with unobservable input	$ 8,849	$ 8,404	$ 7,154
Recurring | Convertible Preferred Securities | Market approach
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Assets, fair value measurement with unobservable input	$ 8,849	8,404
Nonrecurring | Trade | Frac Sand Assets [Member] | Third party appraisal
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Assets, fair value measurement with unobservable input		16,546
Nonrecurring | Trade | Real Property | Market approach
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Assets, fair value measurement with unobservable input		608
Nonrecurring | Trade | Equity Method Investments [Member] | Discounted cash flow analysis
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Assets, fair value measurement with unobservable input		$ 12,424