Equity Investees (Schedule of Operations for Equity Investees) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
INCOME STATEMENT DATA:
Revenues	$ 521,219	$ 539,923
Operating income	28,021	59,162
Net income	(34,224)	24,909
Equity Method Investment, Nonconsolidated Investee or Group of Investees | Poseidon
INCOME STATEMENT DATA:
Revenues	42,413	32,892
Operating income	32,161	23,606
Net income	$ 31,145	$ 21,583