Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator:
Net income attributable to Acadia	$ 9,225	$ 12,867	$ 24,309	$ 40,558
Less: net income attributable to participating securities	(66)	(135)	(158)	(488)
Income from continuing operations net of income attributable to participating securities	$ 9,159	$ 12,732	$ 24,151	$ 40,070
Denominator:
Weighted average shares for basic earnings per share (in shares)	81,565,805	83,699,850	82,245,020	83,665,749
Effect of dilutive securities:
Employee unvested restricted shares (in shares)	0	0	0	3,577
Denominator for diluted earnings per share (in shares)	81,565,805	83,699,850	82,245,020	83,669,326
Basic and diluted earnings per share (in dollars per share)	$ 0.11	$ 0.15	$ 0.29	$ 0.48
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	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	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	140,343	136,593	140,343
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)	474,278	487,299	474,278	481,878
Restricted shares
Anti-Dilutive Shares Excluded from Denominator:
Antidilutive securities excluded from computation of earnings per share (in shares)	38,450	43,202	37,180	0

Anti-dilutive shares excluded from denominator.

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Dilutive securities, effect on basic earnings per share, denominator.

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Earnings per share, numerator.

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Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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The amount of net income or loss for the period per each share in instances when basic and diluted earnings per share are the same amount and reported as a single line item on the face of the financial statements. Basic earnings per share is the amount of net income or loss for the period per each share of common stock or unit outstanding during the reporting period. Diluted earnings per share includes the amount of net income or loss for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Amount after tax of income (loss) from continuing operations attributable to the parent.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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The earnings that is allocated to common stock and participating securities to the extent that each security may share in earnings as if all of the earnings for the period had been distributed.

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