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		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Numerators:
Net income available for Common Shares – basic	$ 36,673	$ 25,746	$ 95,644	$ 89,328
Amounts allocated to dilutive securities	3,136	2,219	8,191	7,929
Net income available for Common Shares – fully diluted	$ 39,809	$ 27,965	$ 103,835	$ 97,257
Denominator:
Weighted average Common Shares outstanding – basic (shares)	84,057	83,531	84,016	83,295
Effect of dilutive securities:
Redemption of Common OP Units for Common Shares (shares)	7,212	7,254	7,220	7,471
Stock options and restricted shares (shares)	671	743	641	705
Weighted average Common Shares outstanding – fully diluted (shares)	91,940	91,528	91,877	91,471
Earnings per Common Share – Basic:
Net income available for Common Shares (usd per share)	$ 0.44	$ 0.31	$ 1.14	$ 1.07
Earnings Per Share, Diluted [Abstract]
Net income available for Common Shares (usd per share)	$ 0.43	$ 0.31	$ 1.13	$ 1.06