Earnings per share - Computation of Basic and Diluted Net Income per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share [Abstract]
Net income	$ 7,918	$ 8,120
Income attributable to noncontrolling interests	(79)	(110)
Preferred stock dividends	(7,045)	(7,045)
Earnings attributable to participating securities	(5,285)	(1,596)
Net loss available to common stockholders after allocation to participating securities	$ (4,491)	$ (631)
Weighted average shares outstanding - basic (in shares)	64,442	58,038
Effect of Class O units, TSR units, FFO units and options to purchase Class A common stock on an "as if" converted basis (in shares)	0	0
Weighted average shares outstanding - diluted (in shares)	64,442	58,038
Basic net loss per share (in dollars per share)	$ (0.07)	$ (0.01)
Diluted net loss per share (in dollars per share)	$ (0.07)	$ (0.01)