Summary of Significant Accounting Policies (Accounting Pronouncements) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounts and other receivables	$ 389,240		$ 373,471
Allowance for credit losses	35,869		19,651	$ 20,222	$ 18,633
Retained earnings	$ (5,201,195)		(5,438,930)
Cumulative Effect
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses			$ 9,503
ASU 2016-13 | Adjusted Balance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounts and other receivables		$ 15,000
Allowance for credit losses		10,000
Retained earnings		$ 22,000