Changes in Operations and Non-operating Items Non-Operating Items (Details) - USD ($) $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2018	[1]	Sep. 30, 2018	[1]	Jun. 30, 2018	[1]	Mar. 31, 2018	[1]	Dec. 31, 2017	[1]	Sep. 30, 2017	[1]	Jun. 30, 2017	[1]	Mar. 31, 2017	[1]	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Changes in Operations and Non-Operating Items [Abstract]
Loss on extinguishments and modification of debt									$ 0		$ 1,435		$ 0		$ 19,052		$ 0		$ 20,487	[1]	$ 0
(Loss) gain on investment transactions, net	$ 0		$ (5,001)		$ 0		$ 3,888		(2,486)		5,667		0		4,950		(1,113)	[1]	8,131	[1]	0
Write-downs of investments									(12,694)		0		(58,800)		(122,000)		0		(193,494)	[1]	0
Other non-operating gain, net	$ 15		$ (38)		$ (26)		$ 117		$ 26		$ 0		$ 71		$ (26)		68	[1]	71	[1]	5,427
Total non-operating (loss) gain, net																	$ (1,045)		$ (205,779)		$ 5,427

[1] See Note 3 to the Company’s consolidated financial statements for information pertaining to non-operating items recorded in 2018 and 2017.