Earnings Per Common Share Calculation of numerator and denominator in eps table (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Earnings Per Share Disclosure [Line Items]
Net income (loss) available for Common Shares – basic	$ 35,024	$ 12,431
Amounts allocated to dilutive securities	3,133	1,191
Net income (loss) available for Common Shares – fully diluted	$ 38,157	$ 13,622
Weighted average Common Shares outstanding - basic	41,513	41,088
Redemption of Common OP Units for Common Shares	3,729	3,980
Employee stock options and restricted shares	288	301
Weighted average Common Shares outstanding - fully diluted	45,530	45,369
Net income (loss) available for Common Shares	$ 0.84	$ 0.30
Net income (loss) available for Common Shares	$ 0.84	$ 0.30