Shareholders' Equity / Partners' Capital - Class B Common Shares (Details) - Class B common shares	12 Months Ended
Dec. 31, 2019 Vote shares
Class of Stock [Line Items]
Common shares entitled to vote \| Vote	50
2012 Offering \| AH LLC \| 2,770 Property Contribution
Class of Stock [Line Items]
Common stock issued in connection with investment (in shares) \| shares	635,075
Maximum
Class of Stock [Line Items]
Voting interest percent	30.00%

Number of shares of stock issued as of the balance sheet date, including shares that had been issued and were previously outstanding but which are now held in the treasury.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21463-112644

Name:	us-gaap_SharesIssued
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant