Leases - Summary of minimum future rental payments required (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Operating Leases
2020	$ 4,682	$ 17,149
2021	17,004	17,004
2022	16,867	16,867
2023	11,055	11,055
2024	9,068	9,068
Thereafter	131,347	131,347
Total undiscounted rental payments	190,023	202,490
Less imputed interest	(99,597)	(102,085)
Total lease liabilities	$ 90,426	$ 100,405
Weighted average remaining lease term, operating leases	31 years 9 months 18 days	31 years
Weighted average incremental borrowing rate, operating leases	7.80%	7.70%
Operating Lease, Liability, Statement of Financial Position [Extensible List]	mac:OperatingandFinanceLeaseLiability	mac:OperatingandFinanceLeaseLiability
Finance Leases
2020	$ 2,043	$ 2,106
2021	10,784	10,441
2022	2,762	2,418
2023	344	0
2024	3,085	0
Thereafter	0	0
Total undiscounted rental payments	19,018	14,965
Less imputed interest	(2,641)	(1,169)
Total lease liabilities	$ 16,377	$ 13,796
Weighted average remaining lease term, finance leases	2 years 1 month 6 days	1 year 7 months 6 days
Weighted average incremental borrowing rate, finance leases	3.70%	4.20%
Finance Lease, Liability, Statement of Financial Position [Extensible List]	mac:OperatingandFinanceLeaseLiability	mac:OperatingandFinanceLeaseLiability

Finance Lease, Liability, to be Paid, after Year Four

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Lessee, Operating Lease, Liability, to be Paid, after Year Four

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No definition available.

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Present value of lessee's discounted obligation for lease payments from finance lease.

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Amount of lessee's undiscounted obligation for lease payments for finance lease.

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Amount of lessee's undiscounted obligation for lease payment for finance lease to be paid in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of lessee's undiscounted obligation for lease payment for finance lease to be paid in fourth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of lessee's undiscounted obligation for lease payment for finance lease to be paid in third fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

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Amount of lessee's undiscounted obligation for lease payment for finance lease to be paid in second fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of lessee's undiscounted obligation for lease payment for finance lease to be paid in remainder of current fiscal year.

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- Definition

Indicates line item in statement of financial position that includes finance lease liability.

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Amount of lessee's undiscounted obligation for lease payments in excess of discounted obligation for lease payments for finance lease.

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Weighted average discount rate for finance lease calculated at point in time.

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Weighted average remaining lease term for finance lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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- Definition

Amount of lessee's undiscounted obligation for lease payment for operating lease.

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Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in fourth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in third fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in second fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of lessee's undiscounted obligation for lease payment for operating lease having initial or remaining lease term in excess of one year to be paid in remainder of current fiscal year.

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Amount of lessee's undiscounted obligation for lease payments in excess of discounted obligation for lease payments for operating lease.

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Present value of lessee's discounted obligation for lease payments from operating lease.

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Indicates line item in statement of financial position that includes operating lease liability.

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Weighted average discount rate for operating lease calculated at point in time.

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Weighted average remaining lease term for operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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