Noncontrolling Interests (Details) (USD $) In Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Equity Rollforward [Line Items]
Beginning Balance			$ 665,474
Contributions			1,459	11,180
Net Income (Loss) Attributable to Parent	79,112	23,432	102,455	37,845
Windfall tax provision - share incentive income			872	(159)
Ending Balance	732,016		732,016
Parent [Member]
Equity Rollforward [Line Items]
Beginning Balance			625,013	625,633
Shares issued			1,018	799
Contributions			0	0
Purchase of noncontrolling interests			(5,879)
Redemption value adjustment			691	538
Tax impact of purchase of WPCI Interest				(1,637)
Net Income (Loss) Attributable to Parent			102,455	37,845
Stock based compensation expense			8,628	4,936
Distributions			(42,561)	(40,974)
Windfall tax provision - share incentive income			872	(159)
Change in other comprehensive income			6,367	(9,178)
Share repurchased			(3,255)	(904)
Ending Balance	693,349	616,899	693,349	616,899
Noncontrolling Interest [Member]
Equity Rollforward [Line Items]
Beginning Balance			40,461	6,775
Shares issued			0	0
Contributions			1,459	11,180
Purchase of noncontrolling interests			(1,612)
Redemption value adjustment			0	0
Tax impact of purchase of WPCI Interest				0
Net Income (Loss) Attributable to Parent			(714)	(414)
Stock based compensation expense			0	0
Distributions			(2,164)	(850)
Windfall tax provision - share incentive income				0
Change in other comprehensive income			1,237	(487)
Share repurchased			0	0
Ending Balance	38,667	16,204	38,667	16,204
Redeemable Noncontrolling Interest [Member]
Equity Rollforward [Line Items]
Beginning Balance			7,546	7,692
Redemption value adjustment			(691)	(538)
Net Income (Loss) Attributable to Parent			604	592
Distributions			(676)	(610)
Change in other comprehensive income			9	(17)
Ending Balance	6,792	7,119	6,792	7,119
Total Equity [Member]
Equity Rollforward [Line Items]
Beginning Balance			665,474	632,408
Shares issued			1,018	799
Contributions			1,459	11,180
Purchase of noncontrolling interests			(7,491)
Redemption value adjustment			691	538
Tax impact of purchase of WPCI Interest				(1,637)
Net Income (Loss) Attributable to Parent			101,741	37,431
Stock based compensation expense			8,628	4,936
Distributions			(44,725)	(41,824)
Windfall tax provision - share incentive income			872	(159)
Change in other comprehensive income			7,604	(9,665)
Share repurchased			(3,255)	(904)
Ending Balance	$ 732,016	$ 633,103	$ 732,016	$ 633,103