Shareholders' Equity - Conversion of Series E Convertible Unit into Series D Convertible Units (Details) $ in Thousands		12 Months Ended
	Feb. 29, 2016 USD ($) shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares	Dec. 31, 2014 USD ($)
Class of Stock [Line Items]
Gain on conversion of Series E units | $		$ 11,463	$ 0	$ 0
Series E Convertible Units
Class of Stock [Line Items]
Contingent beneficial conversion, Series E | $	$ 2,800	$ 2,800
Series E Convertible Units | Operating Partnership
Class of Stock [Line Items]
Units owned (in shares)	4,375,000
Series E Convertible Units | AH LLC
Class of Stock [Line Items]
Units owned (in shares)		0	4,375,000
Series E Convertible Units | AH LLC | Operating Partnership
Class of Stock [Line Items]
Units owned (in shares)	4,375,000
Business acquisition, equity interest issued or issuable, number of shares, multiplier	1