Shareholders' Equity - Conversion of Series D Convertible Units into Class A Units (Details) $ / shares in Units, $ in Millions			12 Months Ended
	Sep. 30, 2016 USD ($) shares	Feb. 29, 2016 USD ($) shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 shares
Series E Convertible Units
Class of Stock [Line Items]
Contingent beneficial conversion, Series E | $		$ 2.8	$ 2.8
Series D Convertible Units
Class of Stock [Line Items]
Percent of distributions claimed on operating partnership			70.00%
Period after issuance for eligibility to participate in operating partnership distributions			30 months
Limited liability company or limited partnership, conversion requirements, adjusted funds from operations (in dollars per share) | $ / shares			$ 0.80
Limited liability company or limited partnership, conversion requirements, average price per common share (in dollars per share) | $ / shares			$ 18.00
Contingent beneficial conversion, Series E | $	$ 7.6
Operating Partnership | Series E Convertible Units
Class of Stock [Line Items]
Units owned (in shares)		4,375,000
Operating Partnership | Series D Convertible Units
Class of Stock [Line Items]
Units owned (in shares)	8,750,000
AH LLC | Series E Convertible Units
Class of Stock [Line Items]
Units owned (in shares)			0	4,375,000
AH LLC | Series D Convertible Units
Class of Stock [Line Items]
Units owned (in shares)			0	4,375,000
AH LLC | Operating Partnership | Series E Convertible Units
Class of Stock [Line Items]
Units owned (in shares)		4,375,000
AH LLC | Operating Partnership | Series D Convertible Units
Class of Stock [Line Items]
Limited liability company or limited partnership, conversion ratio	1		1