Indebtedness (Tables)

3 Months Ended

Mar. 31, 2013

Debt Disclosure [Abstract]

Fair Value, Liabilities Measured on a Recurring Basis, Disclosure Only

	Book Value at 12/31/12		Book Value at 3/31/13		Fair Value at 12/31/12		Issuances and Assumptions		Payments/Payoffs			Adjustments to Fair Value			Fair Value at 3/31/13
Fixed rate secured debt	$	1,149,541	$	1,131,398	$	1,251,477	$	—	$	(17,486	)	$	20,784		$	1,254,775
Variable rate secured debt	18,412		20,262		18,386		1,933		—			(83		)	20,236
Unsecured notes	2,993,217		3,242,737		3,336,386		250,000		(480		)	8,638			3,594,544
Unsecured line of credit	285,000		—		285,632		—		(285,000		)	(632		)	—
Total	$	4,446,170	$	4,394,397	$	4,891,881	$	251,933	$	(302,966	)	$	28,707		$	4,869,555

Unsecured Lines of Credit

Description	Maximum Capacity		Maturity Date	Outstanding Balance at March 31, 2013
Unsecured Line of Credit - Partnership	$	850,000	December 2015	$	—