Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred income tax assets:
Operating lease obligations	$ 322,122	$ 406,172
Financing lease obligations	90,011	156,913
Operating loss carryforwards	237,728	330,983
Accrued expenses	96,410	54,154
Intangible assets	60,069	11,160
Tax credits	50,356	50,356
Investment in unconsolidated ventures	5,105	0
Capital loss carryforward	2,263	40,723
Other	8,561	8,098
Total gross deferred income tax asset	872,625	1,058,559
Valuation allowance	(380,990)	(408,903)
Net deferred income tax assets	491,635	649,656
Deferred income tax liabilities:
Operating lease right-of-use assets	(277,489)	(328,100)
Property, plant and equipment	(223,703)	(303,853)
Investment in unconsolidated ventures	0	(33,100)
Total gross deferred income tax liability	(501,192)	(665,053)
Net deferred tax asset (liability)	$ (9,557)	$ (15,397)

The tax effect as of the balance sheet date of the amount of the estimated future tax deductions arising from differences in accounting under GAAP and tax returns for assets and liabilities established under GAAP pertaining to capital lease obligations.

No definition available.