Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Long-Term Debt, Capital and Financing Leases and Financing Obligations [Line Items]
Total long-term debt and capital and financing lease obligations	$ 5,135,395	$ 5,142,291
Less current portion	605,006	602,501
Total long-term debt and capital and financing lease obligations, less current portion	4,530,389	4,539,790
Mortgages [Member]
Long-Term Debt, Capital and Financing Leases and Financing Obligations [Line Items]
Total long-term debt and capital and financing lease obligations	3,482,476	3,497,762
Unamortized debt discount	$ 17,100	$ 16,600
Weighted average interest rate	4.64%	4.59%
Capital and Financing Lease Obligations [Member]
Long-Term Debt, Capital and Financing Leases and Financing Obligations [Line Items]
Total long-term debt and capital and financing lease obligations	$ 1,257,085	$ 1,271,554
Weighted average interest rate	7.24%	6.75%
Convertible Debt [Member]
Long-Term Debt, Capital and Financing Leases and Financing Obligations [Line Items]
Total long-term debt and capital and financing lease obligations	$ 313,626	$ 309,853
Principal	316,300	316,300
Unamortized debt discount	$ 2,600	$ 6,400
Weighted average interest rate	2.75%	2.75%
Notes Payable, Insurance Premiums [Member]
Long-Term Debt, Capital and Financing Leases and Financing Obligations [Line Items]
Total long-term debt and capital and financing lease obligations	$ 19,859	$ 0
Weighted average interest rate	3.44%
Other Notes Payable [Member]
Long-Term Debt, Capital and Financing Leases and Financing Obligations [Line Items]
Total long-term debt and capital and financing lease obligations	$ 62,349	$ 63,122
Weighted average interest rate	5.95%	5.98%