Noncontrolling Interest (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 entity trustsubsidiaries	Dec. 31, 2010	Dec. 31, 2009
Noncontrolling Interest
Number of real estate investment trust subsidiaries	2
Number of firms in which entity holds majority ownership interest	5
Fair value of noncontrolling owners equity interests	$ 44,643	$ 45,676	$ 51,381
Redeemable noncontrolling interest
Balance, beginning of period	45,676	51,381	44,811
Net income	1,956	1,779	(1,457)
Distributions to redeemable noncontrolling interest	(2,061)	(2,105)	(2,196)
Additions and redemptions, net	(5,304)	(6,231)	8,192
Adjustments to fair value	5,003	852	2,031
Other	(627)
Balance, end of period	$ 44,643	$ 45,676	$ 51,381