Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Operating properties, accumulated depreciation	$ 275,977	$ 215,856
Notes and accounts receivable, allowance for doubtful accounts	535	1,167
Intangible assets, accumulated amortization	104,931	53,483
Intangible liabilities, accumulated amortization	$ 28,960	$ 12,227
Preferred stock, par value (in usd per share)	$ 1	$ 1
Preferred stock, shares authorized	20,000,000	20,000,000
Preferred stock, shares issued	6,867,357	6,867,357
Preferred stock, shares outstanding	6,867,357	6,867,357
Common stock, par value (in usd per share)	$ 1	$ 1
Common stock, shares authorized	700,000,000	700,000,000
Common stock, shares issued	430,349,620	403,746,938
Treasury stock, shares	10,329,082	10,329,082