Incentive plans - Stock-Based Incentive Plan Activity (Details) - $ / shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning balance (shares)	0	7,799
Granted (shares)	0	0
Vested (shares)	0	(4,516)
Surrendered (shares)	0	(3,283)
Ending balance (shares)	0	0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Beginning balance, Weighted-Average Grant Date Fair Value (usd per share)	$ 0.00	$ 26.46
Granted, Weighted-Average Grant Date Fair Value (usd per share)	0.00	0.00
Vested, Weighted-Average Grant Date Fair Value (usd per share)	0.00	26.46
Surrendered, Weighted-Average Grant Date Fair Value (usd per share)	0.00	26.46
Beginning balance, Weighted-Average Grant Date Fair Value (usd per share)	$ 0.00	$ 0.00
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning balance (shares)	0	91,756
Granted (shares)	0	0
Vested (shares)	0	(53,131)
Surrendered (shares)	0	(38,625)
Ending balance (shares)	0	0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Beginning balance, Weighted-Average Grant Date Fair Value (usd per share)	$ 0.00	$ 19.20
Granted, Weighted-Average Grant Date Fair Value (usd per share)	0.00	0.00
Vested, Weighted-Average Grant Date Fair Value (usd per share)	0.00	19.20
Surrendered, Weighted-Average Grant Date Fair Value (usd per share)	0.00	19.20
Beginning balance, Weighted-Average Grant Date Fair Value (usd per share)	$ 0.00	$ 0.00
LTIP Units
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning balance (shares)	412,795	280,452
Granted (shares)	255,894	146,728
Vested (shares)	(81,112)	(14,385)
Surrendered (shares)	(75,605)	0
Ending balance (shares)	511,972	412,795
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Beginning balance, Weighted-Average Grant Date Fair Value (usd per share)	$ 22.80	$ 22.29
Granted, Weighted-Average Grant Date Fair Value (usd per share)	16.82	25.85
Vested, Weighted-Average Grant Date Fair Value (usd per share)	22.34	36.30
Surrendered, Weighted-Average Grant Date Fair Value (usd per share)	16.35	0.00
Beginning balance, Weighted-Average Grant Date Fair Value (usd per share)	$ 20.84	$ 22.80

Education Realty Trust, Inc. 10-Q