Earnings Per Common Share - Calculation of numerator and denominator in eps table (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Numerators:
Net income available for common stockholders	$ 46,187	$ 46,401	$ 113,062	$ 159,710
Amounts allocated to dilutive securities	2,658	2,676	6,507	9,902
Net income available for common stockholders – fully diluted	$ 48,845	$ 49,077	$ 119,569	$ 169,612
Denominators:
Weighted average common shares outstanding – basic (in shares)	181,833	180,312	181,781	179,938
Effect of dilutive securities:
Exchange of common OP units for common shares (in shares)	10,482	11,286	10,486	11,382
Restricted stock and options (in shares)	227	262	271	226
Weighted average common shares outstanding – fully diluted (in shares)	192,542	191,860	192,538	191,546
Earnings per common share – basic (usd per share)	$ 0.25	$ 0.26	$ 0.62	$ 0.89
Earnings per common share – fully diluted (usd per share)	$ 0.25	$ 0.26	$ 0.62	$ 0.89