Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2015

Accounting Policies [Abstract]

Schedule of Error Corrections and Prior Period Adjustments [Table Text Block]

The accompanying consolidated balance sheet and statement of equity of the Trust has been restated to correct the misclassification as follows (in thousands except share amounts):

	December 31,						January 1,
	2014			2013			2013
Common shares of beneficial interest (as previously reported)	$	150		$	148		$	119
Impact of reclassification	(1		)	(1		)	(1		)
Common shares of beneficial interest (as adjusted and currently reported)	$	149		$	147		$	118
Additional paid-in capital (as previously reported)	$	3,740,594		$	3,669,618		$	2,687,701
Impact of reclassification	(51,950		)	(51,950		)	(51,950		)
Additional paid-in capital (as adjusted and currently reported)	$	3,688,644		$	3,617,668		$	2,635,751
Common shares in treasury, at cost (as previously reported)	$	(51,951	)	$	(51,951	)	$	(51,951	)
Impact of reclassification	51,951			51,951			51,951
Common shares in treasury, at cost (as adjusted and currently reported)	$	—		$	—		$	—
Number of common shares (as previously reported)	149,807,179			147,846,801			119,720,776
Impact of reclassification	(1,249,909		)	(1,249,909		)	(1,249,909		)
Number of common shares (as adjusted and currently reported)	148,557,270			146,596,892			118,470,867

Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block]

The following summarizes the fair value of the Company's mortgage loans and unsecured notes at December 31, 2014 and December 31, 2015 (in thousands):

	Mortgage Loans				Unsecured Notes
	Carrying Value		Fair Value		Carrying Value		Fair Value
As of December 31, 2014	$	484,852	$	501,231	$	2,498,021	$	2,704,069
As of December 31, 2015	$	307,908	$	306,334	$	2,580,108	$	2,616,395

Schedule of New Accounting Pronouncements and Changes in Accounting Principles [Table Text Block]

The following table presents the impact of the change in accounting principle to the consolidated balance sheets of the Trust and the Operating Partnership as of December 31, 2014 (in thousands):

	As of December 31, 2014
	Deferred financing and leasing costs, net			Mortgage loans, net			Unsecured notes, net
As previously reported	$	206,286		$	487,301		$	2,509,094
Impact of change in accounting principle	(13,522		)	(2,449		)	(11,073		)
As adjusted and currently reported	$	192,764		$	484,852		$	2,498,021

The following table presents the impact of the change in accounting principle to the consolidated balance sheets of the Trust and the Operating Partnership as of December 31, 2015 (in thousands):

	As of December 31, 2015
	Deferred financing and leasing costs, net			Mortgage loans, net			Unsecured notes, net
As would have been reported prior to change in accounting principle	$	206,327		$	309,711		$	2,592,523
Impact of change in accounting principle	(14,218		)	(1,803		)	(12,415		)
As reported	$	192,109		$	307,908		$	2,580,108