Commitments and Contingencies (Other Commitments) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Operating
2021 (remaining three months)	$ 1,728		$ 1,728		$ 3,797
2022	6,635		6,635		6,756
2023	6,272		6,272		6,393
2024	6,188		6,188		6,309
2025	6,176		6,176		6,297
Thereafter	334		334		496
Total undiscounted cash flows	27,333		27,333		30,048
Present value discount	(2,717)		(2,717)		(3,771)
Other adjustments	22,495		22,495		23,795
Lease liabilities	47,111		47,111		50,072
Finance
2021 (remaining six months)	1,384		1,384		5,494
2022	5,604		5,604		5,604
2023	5,716		5,716		5,716
2024	5,830		5,830		5,830
2025	5,946		5,946		5,946
Thereafter	1,567,826		1,567,826		1,567,826
Total undiscounted cash flows	1,592,306		1,592,306		1,596,416
Present value discount	(1,439,677)		(1,439,677)		(1,445,896)
Other adjustments	0		0		0
Lease liabilities	$ 152,629		$ 152,629		$ 150,520
Operating leases, weighted average incremental borrowing rate, discount rate (percent)	5.00%		5.00%
Operating leases, weighted average lease term (in years)	7 years 7 months 6 days		7 years 7 months 6 days
Operating lease payments made	$ 800	$ 1,000	$ 2,100	$ 3,200
Operating leases, excluding tenant paid leases, weighted average lease term			4 years 10 months 24 days		5 years 7 months 6 days
Operating leases, weighted average incremental borrowing rate, discount rate	4.70%		4.70%		5.00%
Finance lease payments made	$ 1,300	1,400	$ 4,100	4,000
Finance leases, weighted average rate implicit in the lease, discount rate (percent)	5.50%		5.50%		5.50%
Finance leases, weighted average lease term (in years)	96 years 2 months 12 days		96 years 2 months 12 days
Finance leases, weighted average lease term					97 years
Interest Expense
Finance
Finance lease, interest expense	$ 2,100	2,000	$ 6,200	6,100
Depreciation and Amortization
Finance
Finance lease, amortization	$ 400	$ 400	$ 1,100	$ 1,100