Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred income tax assets:
Capital and financing lease obligations	$ 165,703	$ 264,255
Operating loss carryforwards	298,255	288,469
Deferred lease liability	63,263	52,869
Accrued expenses	61,309	66,123
Tax credits	50,462	49,556
Capital loss carryforward	41,413	0
Intangible assets	10,133	14,493
Other	2,872	7,190
Total gross deferred income tax asset	693,410	742,955
Valuation allowance	(336,417)	(336,087)
Net deferred income tax assets	356,993	406,868
Deferred income tax liabilities:
Property, plant and equipment	(334,145)	(477,512)
Investment in unconsolidated ventures	(41,219)	0
Total gross deferred income tax liability	(375,364)	(477,512)
Net deferred tax liability	$ (18,371)	$ (70,644)