Financial Instruments (Narrative) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 31,848	$ 1,868,922
Customers' advances for construction	99,447	95,556
Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans payable	381,005	25,724
Mutual funds	22,959	23,419
Cash and cash equivalents	$ 31,848	$ 1,868,922