Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Parent Company [Member]
Net income	$ 19,820	$ 14,541	$ 57,903	$ 41,608
Other comprehensive income (loss):
Amortization of loss on settlement of derivative instruments recognized in net income	2,366	2,366	7,099	7,099
Effective portion of change in fair value of derivative instruments	(25)	0	(85)	0
Less reclassification adjustment for change in fair value of derivative instruments included in net income	8	0	17	0
Other comprehensive income	2,349	2,366	7,031	7,099
Comprehensive income	22,169	16,907	64,934	48,707
Less: comprehensive income (loss) attributable to noncontrolling interests:
Net income attributable to noncontrolling interests	251	1,112	123	3,296
Other comprehensive (loss) income attributable to noncontrolling interests	(4)	4	(20)	14
Comprehensive income attributable to noncontrolling interests	247	1,116	103	3,310
Comprehensive income attributable to the Company/Partnership	21,922	15,791	64,831	45,397
Partnership Interest [Member]
Net income	19,820	14,541	57,903	41,608
Other comprehensive income (loss):
Amortization of loss on settlement of derivative instruments recognized in net income	2,366	2,366	7,099	7,099
Effective portion of change in fair value of derivative instruments	(25)	0	(85)	0
Less reclassification adjustment for change in fair value of derivative instruments included in net income	8	0	17	0
Other comprehensive income	2,349	2,366	7,031	7,099
Comprehensive income	22,169	16,907	64,934	48,707
Less: comprehensive income (loss) attributable to noncontrolling interests:
Net income attributable to noncontrolling interests	212	154	636	425
Other comprehensive (loss) income attributable to noncontrolling interests	(9)	0	(34)	0
Comprehensive income attributable to noncontrolling interests	203	154	602	425
Comprehensive income attributable to the Company/Partnership	21,966	16,753	64,332	48,282
Limited Partners [Member] | Partnership Interest [Member]
Net income			116	77
Other comprehensive income (loss):
Other comprehensive income			$ 14	$ 14