Fair Value Measurements (Financial Assets And Liabilities Measured At Fair Value On Recurring Basis) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Construction Reserve Funds	$ 161,865		$ 161,865		$ 255,408
Exchange Option Liability on Subsidiary Convertible Senior Notes	8,938		8,938		$ 5,611
Marketable security gains (losses), net	(8,000)	$ (1,700)	(56,800)	$ (1,300)
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	78,717		78,717
Derivative instruments (included in other receivables)	51		51
Construction Reserve Funds	161,865		161,865
Short sales of marketable securities	2,745		2,745
Derivative instruments (included in other current liabilities)	1,479		1,479
Exchange Option Liability on Subsidiary Convertible Senior Notes	0		0
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	0		0
Derivative instruments (included in other receivables)	0		0
Construction Reserve Funds	0		0
Short sales of marketable securities	0		0
Derivative instruments (included in other current liabilities)	481		481
Exchange Option Liability on Subsidiary Convertible Senior Notes	0		0
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	0		0
Derivative instruments (included in other receivables)	0		0
Construction Reserve Funds	0		0
Short sales of marketable securities	0		0
Derivative instruments (included in other current liabilities)	0		0
Exchange Option Liability on Subsidiary Convertible Senior Notes	$ 8,938		$ 8,938