Compensation plans - Equity-based compensation (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Less amounts capitalized	$ (3,418)	$ (4,470)	$ (7,929)
Equity-based compensation	9,207	8,290	36,396
Share-settled
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-settled equity-based compensation, gross	11,635	12,760	44,325
Less amounts capitalized	(3,418)	(4,470)	(7,929)
Equity-based compensation	8,217	8,290	36,396
Restricted stock awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-settled equity-based compensation, gross	8,839	13,169	25,271
Performance share awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-settled equity-based compensation, gross	2,545	(1,250)	15,192
Outperformance share award
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-settled equity-based compensation, gross	174	101	0
Stock option awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-settled equity-based compensation, gross	77	740	3,862
Cash-settled
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-settled equity-based compensation, gross	1,153	0	0
Less amounts capitalized	(163)	0	0
Equity-based compensation	990	0	0
Phantom unit awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-settled equity-based compensation, gross	404	0	0
Performance unit awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-settled equity-based compensation, gross	$ 749	$ 0	$ 0

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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