MAALP Capital (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
General Partners' Capital Account [Member]
Increase (Decrease) in Partners' Capital [Roll Forward]
Units Issued During Period, Value, Unit Options Exercised		$ 218
Total Partnership Capital [Member]
Increase (Decrease) in Partners' Capital [Roll Forward]
Units Issued During Period, Value, Unit Options Exercised	$ 916	218
Limited Partner [Member]
Capital Disclosure [Line Items]
Noncontrolling Interest in Joint Ventures	2,306	2,306	$ 2,306	$ 2,306
Increase (Decrease) in Partners' Capital [Roll Forward]
Dividends, Preferred Stock, Cash	2,766	2,766
Limited Partner [Member] \| General Partners' Capital Account [Member]
Increase (Decrease) in Partners' Capital [Roll Forward]
Beginning Balance	6,270,758	6,337,721	6,337,721
Net Income Allocated to General Partners	158,851	202,163
Issuance of units	(271)	154
Units repurchased and retired	(2,912)	(4,782)
Units Issued During Period, Value, Unit Options Exercised	916
General partner units issued in exchange for limited partner units	4,283	1,133
Units issued in exchange for redeemable units	1,915	1,482
Redeemable stock fair market value	121	(870)
Adjustment for noncontrolling interest ownership in operating partnership	226	68
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	(233)
Amortization of unearned compensation	9,877	8,438
Distributions	(315,012)	(296,535)
Ending Balance	6,128,519	6,249,190	6,270,758	6,337,721
Limited Partner [Member] \| Total Partnership Capital [Member]
Increase (Decrease) in Partners' Capital [Roll Forward]
Beginning Balance	6,573,875	6,642,082	6,642,082
Net Income Available for Common Unitholders	167,505	212,529
Other comprehensive (loss) income - derivatives insturments (cash flow hedges)	9,501	(368)
Issuance of units	(271)	2,161
Units repurchased and retired	(2,912)	(4,782)
General partner units issued in exchange for limited partner units	0	0
Units issued in exchange for redeemable units	1,915	1,482
Redeemable stock fair market value	121	(870)
Adjustment for noncontrolling interest ownership in operating partnership	0	0
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	0
Amortization of unearned compensation	9,877	8,438
Distributions	(326,226)	(307,517)
Dividends, Preferred Stock, Cash	2,766	2,766
Ending Balance	6,431,535	6,550,607	6,573,875	6,642,082
Limited Partner [Member] \| Limited Partner [Member]
Increase (Decrease) in Partners' Capital [Roll Forward]
Beginning Balance	231,676	235,976	235,976
Net Income Allocated to Limited Partners	5,888	7,600
General partner units issued in exchange for limited partner units	(4,283)	(1,133)
Adjustment for noncontrolling interest ownership in operating partnership	(226)	(68)
Distributions	(11,214)	(10,982)
Ending Balance	221,841	231,393	231,676	235,976
Limited Partner [Member] \| AOCI Attributable to Noncontrolling Interest [Member]
Increase (Decrease) in Partners' Capital [Roll Forward]
Beginning Balance	2,295	1,246	1,246
Other comprehensive (loss) income - derivatives insturments (cash flow hedges)	9,501	(368)
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	233
Ending Balance	12,029	878	2,295	1,246
Accumulated Distributions in Excess of Net Income [Member] \| Limited Partner [Member]
Increase (Decrease) in Partners' Capital [Roll Forward]
Issuance of units	0	2,007	$ 66,840	$ 64,833
Dividends, Preferred Stock, Cash	2,766	2,766
Preferred Stock Including Additional Paid in Capital [Member] \| Limited Partner [Member]
Increase (Decrease) in Partners' Capital [Roll Forward]
Ending Balance	$ 66,840	$ 66,840

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[Line Items] for Capital Disclosure [Table]

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Distributions

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Fair value option and measurement.

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General Partnership Units Issued in Exchange for Limited Partnership Units

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Net Income Available for Common Unitholders

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Partnership units issued in exchange for redeemable units

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Units Issued During Period, Value, New Issues

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Units Issued During Period, Value, Unit Options Exercised

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Units Repurchased and Retired During Period, Value

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Amount of paid and unpaid preferred stock dividends declared with the form of settlement in cash.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Carrying amount of the equity interests owned by noncontrolling shareholders, partners, or other equity holders in joint ventures included in the entity's consolidated financial statements.

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Net Increase or Decrease in balance of noncontrolling interest in the subsidiary during the reporting period.

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Aggregate amount of net income allocated to general partners.

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Aggregate amount of net income allocated to limited partners.

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Amount after tax and reclassification adjustments, of increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

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The amount of ownership interest of different classes of partners in limited partnership.

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