Quarterly Financial Data (Unaudited) Quarterly Financial Data (unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	1 Months Ended		3 Months Ended								12 Months Ended
	Dec. 31, 2012	Jan. 31, 2012	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Quarterly Financial Data (unaudited) [Abstract]
Revenues			$ 191,432	$ 187,310	$ 178,212	$ 170,954	$ 158,888	$ 157,728	$ 153,992	$ 150,466	$ 727,908	$ 621,074	$ 568,072
Net income attributable to common shareholders			142,166	30,703	21,763	88,758	46,850	11,840	(16,597)	7,286	283,390	49,379	23,216
Net income attributable to common shareholders per share - basic			$ 1.63	$ 0.36	$ 0.26	$ 1.10	$ 0.63	$ 0.16	$ (0.23)	$ 0.10	$ 3.35	$ 0.67	$ 0.33
Net income attributable to common shareholders per share – diluted			$ 1.60	$ 0.35	$ 0.26	$ 1.07	$ 0.62	$ 0.16	$ (0.23)	$ 0.10	$ 3.30	$ 0.66	$ 0.33
Gain on sale of discontinued operations, net of tax			82,527			32,541	24,621				115,068	24,621	9,614
Income Loss From Disposition Of Discontinued Operations Per Basic Share			$ 0.96			$ 0.41	$ 0.33
Income Loss From Disposition Of Discontinued Operations Per Diluted Share			$ 0.94			$ 0.39	$ 0.33
Gain on acquisition of controlling interest in joint ventures	17,200	40,200	17,227			40,191					57,418	0	0
Income loss from acquisition of the remaining non-controlling ownership interest per basic share			$ 0.20			$ 0.50
Income loss from acquisition of the remaining non-controlling ownership interest per diluted share			$ 0.20			$ 0.49
Gain (loss) on sale of unconsolidated JV property			14,543	2,875			6,394
Income Loss From Disposition Of Unconsolidated Joint Venture Property Per Basic Share			$ 0.17	$ 0.03			$ 0.09
Income Loss From Disposition Of Unconsolidated Joint Venture Property Per Diluted Share			$ 0.17	$ 0.03			$ 0.09
Loss on discontinuation of hedging relationship									29,791		0	29,791	0
Loss from discontinuation of hedging relationship per basic share								$ 0
Loss from discontinuation of hedging relationship per diluted share									$ 0.41
Gain on sale of properties, including land									$ 4,748		$ 0	$ 4,748	$ 236
Income loss from sale of undeveloped land to a joint venture per basic share									$ 0.07
Income loss from sale of undeveloped land to a joint venture per diluted share									$ 0.07