Schedule III - Real Estate and Accumulated Depreciation - Summary of Changes in Accumulated Depreciation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Changes in accumulated depreciation
Balance, beginning of year	$ 5,360,389	$ 6,084,616	$ 5,432,805
Depreciation	743,749	705,649	765,895
Dispositions and other	(63,760)	(1,429,876)	(114,084)
Balance, end of year	$ 6,040,378	$ 5,360,389	$ 6,084,616