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, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Numerators:
Net income available for Common Shares – basic	$ 31,786	$ 25,483	$ 58,972	$ 63,582
Amounts allocated to dilutive securities	2,724	2,229	5,054	5,710
Net income available for Common Shares – fully diluted	$ 34,510	$ 27,712	$ 64,026	$ 69,292
Denominator:
Weighted average Common Shares outstanding – basic (shares)	84,031	83,234	83,996	83,175
Effect of dilutive securities:
Redemption of Common OP Units for Common Shares (shares)	7,221	7,530	7,223	7,582
Stock options and restricted shares (shares)	599	656	610	654
Weighted average Common Shares outstanding – fully diluted (shares)	91,851	91,420	91,829	91,411
Earnings per Common Share – Basic:
Net income available for Common Shares (usd per share)	$ 0.38	$ 0.31	$ 0.70	$ 0.76
Earnings Per Share, Diluted [Abstract]
Net income available for Common Shares (usd per share)	$ 0.38	$ 0.30	$ 0.70	$ 0.76