The increase during the period in capital lease obligations due to entering into new capital leases.

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Recently Issued Accounting Literature (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change						$ 14,519
Earnings less than distributions	$ (4,135,602)		$ (4,135,602)			$ (4,183,253)
Increase (decrease) in fair value of marketable securities	(7,699)	$ 0	(24,801)	$ 0
Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Earnings less than distributions					$ (111,225)
Increase (decrease) in fair value of marketable securities	(7,699)		(24,801)
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Capitalized leasing costs	$ 1,444	$ 3,883	$ 1,280	$ 3,494
Retained Earnings \| Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change					$ 14,519