Financial Instruments (Narrative) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 7,227	$ 1,868,922
Customers' advances for construction	100,584	95,556
Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans payable	15,000	25,724
Mutual funds	22,794	23,419
Cash and cash equivalents	$ 7,227	$ 1,868,922