Financial Instruments (Narrative) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 8,494	$ 1,868,922
Customers' advances for construction	105,613	95,556
Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans payable	47,185	25,724
Mutual funds	24,855	23,419
Cash and cash equivalents	$ 8,494	$ 1,868,922