Equity Investees (Schedule of Balance Sheet Information for Equity Investees) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
ASSETS
Current assets	$ 580,169	$ 593,074
Fixed assets, net	3,851,334	4,294,475
Total assets	5,933,619	6,597,641	$ 6,479,071
LIABILITIES AND PARTNERS’ CAPITAL
Current liabilities	383,411	415,495
Total liabilities and equity	5,933,619	6,597,641
Equity Method Investment, Nonconsolidated Investee or Group of Investees
ASSETS
Current assets	42,565	44,129
Fixed assets, net	299,315	321,752
Other assets	25,654	16,739
Total assets	367,534	382,620
LIABILITIES AND PARTNERS’ CAPITAL
Current liabilities	13,411	20,081
Other liabilities	248,857	252,331
Equity	105,266	110,208
Total liabilities and equity	$ 367,534	$ 382,620