Fair Value (Assets and Liabilities Not Measured at Fair Value) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Assets:
Cash and Restricted cash	$ 1,282,744	$ 1,242,997	$ 1,188,284	$ 620,135
Liabilities:
Variable-rate debt	1,768,062	1,945,344
Allowance for accounts receivable	30,600	33,000
Notes receivable
Liabilities:
Allowance for notes receivable	200	200
Fair Value Hierarchy Level 1 | Carrying Amount
Assets:
Cash and Restricted cash	1,282,744	1,242,997
Fair Value Hierarchy Level 1 | Estimated Fair Value
Assets:
Cash and Restricted cash	1,282,744	1,242,997
Fair Value Hierarchy Level 3 | Carrying Amount
Assets:
Accounts receivable, net	81,503	66,726
Notes receivable, net	3,235	622
Fair Value Hierarchy Level 3 | Estimated Fair Value
Assets:
Accounts receivable, net	81,503	66,726
Notes receivable, net	3,235	622
Fair Value Hierarchy Level 2 | Carrying Amount
Liabilities:
Fixed-rate debt	2,726,121	2,374,822
Variable-rate debt	1,768,062	1,945,344
Fair Value Hierarchy Level 2 | Estimated Fair Value
Liabilities:
Fixed-rate debt	2,766,762	2,461,155
Variable-rate debt	$ 1,768,062	$ 1,945,344