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, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Numerator:
Net income available for Common Stockholders – basic	$ 39,498	$ 35,490	$ 96,385	$ 86,073
Amounts allocated to dilutive securities	2,649	2,998	6,539	7,308
Net income available for Common Stockholders – fully diluted	$ 42,147	$ 38,488	$ 102,924	$ 93,381
Denominator:
Weighted average Common Shares outstanding – basic (shares)	86,763	84,516	86,408	84,419
Effect of dilutive securities:
Redemption of Common OP Units for Common Shares (shares)	5,886	7,205	6,235	7,206
Stock options and restricted shares (shares)	414	543	398	538
Weighted average Common Shares outstanding – fully diluted (shares)	93,063	92,264	93,041	92,163
Earnings per Common Share – Basic:
Net income available for Common Shares (usd per share)	$ 0.46	$ 0.42	$ 1.12	$ 1.02
Earnings per Common Share – Fully Diluted:
Net income available for Common Shares (usd per share)	$ 0.45	$ 0.42	$ 1.11	$ 1.01