Changes in Operations and Non-operating Items Non-Operating Items (Details) - USD ($) $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2017	[1]	Sep. 30, 2017	[1]	Jun. 30, 2017	[1]	Mar. 31, 2017	[1]	Dec. 31, 2016	[1]	Sep. 30, 2016	[1]	Jun. 30, 2016	[1]	Mar. 31, 2016	[1]	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Changes in Operations and Non-Operating Items [Abstract]
Loss on extinguishments and modification of debt	$ 0		$ (1,435)		$ 0		$ (19,052)										$ (20,487)	[1]	$ 0		$ (37,040)
Gain on investment transactions, net	(2,486)		5,667		0		4,950										8,131	[1]	0		12,173
Write-downs of investments	(12,694)		0		(58,800)		(122,000)										(193,494)	[1]	0		0
Other non-operating gain, net	$ 26		$ 0		$ 71		$ (26)		$ 4,949		$ 57		$ (75)		$ 496		71	[1]	5,427	[1]	7,228
Total non-operating (loss) gain, net																	$ (205,779)		$ 5,427		$ (17,639)

[1] See Note 5 to the Company’s consolidated financial statements for information pertaining to non-operating items recorded in 2017 and 2016.