Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator:
Net income attributable to Acadia									$ 61,470	$ 72,776	$ 65,708
Less: net income attributable to participating securities									(642)	(793)	(927)
Income from continuing operations net of income attributable to participating securities									$ 60,828	$ 71,983	$ 64,781
Denominator:
Weighted average shares for basic earnings per share (in shares)									83,682,789	76,231,000	68,851,083
Effect of dilutive securities:
Employee unvested restricted shares (in shares)									2,682	12,550	18,556
Denominator for diluted earnings per share (in shares)	83,733,000	83,700,000	83,662,000	83,646,000	82,728,000	78,624,000	72,896,000	71,215,000	83,685,471	76,243,550	68,869,639
Basic and diluted earnings per share (in dollars per share)									$ 0.73	$ 0.94	$ 0.94
Series A Preferred OP Units
Anti-Dilutive Shares Excluded from Denominator:
Antidilutive securities excluded from computation of earnings per share (in shares)									188	188	188
Series A Preferred OP Units - Common share equivalent
Anti-Dilutive Shares Excluded from Denominator:
Antidilutive securities excluded from computation of earnings per share (in shares)									25,067	25,067	25,067
Series C Preferred OP Units
Anti-Dilutive Shares Excluded from Denominator:
Antidilutive securities excluded from computation of earnings per share (in shares)									136,593	141,593	0
Series C Preferred OP Units - Common share equivalent
Anti-Dilutive Shares Excluded from Denominator:
Antidilutive securities excluded from computation of earnings per share (in shares)									479,978	410,207	0