Shareholders' Equity - Conversion of Series E Convertible Units in Series D Convertible Units (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016 USD ($) shares	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) shares	Jun. 30, 2015 USD ($)	Feb. 29, 2016 shares	Dec. 31, 2015 shares
Class of Stock [Line Items]
Gain on conversion of Series E units | $	$ 0	$ 0	$ 11,463	$ 0
AH LLC | Series E Convertible Units
Class of Stock [Line Items]
Ownership units owned (in shares)	0		0			4,375,000
AH LLC | Series E Convertible Units | Operating Partnership
Class of Stock [Line Items]
Ownership units owned (in shares)					4,375,000
Ownership units exchange ratio					1
AH LLC | Series D Convertible Units
Class of Stock [Line Items]
Ownership units owned (in shares)	8,750,000		8,750,000			4,375,000
AH LLC | Series D Convertible Units | Operating Partnership
Class of Stock [Line Items]
Ownership units owned (in shares)	8,750,000		8,750,000			4,375,000