Indebtedness (Details Textual) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended			6 Months Ended			6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Apr. 16, 2012 2012 Notes [Member]	Jun. 30, 2012 2028 Notes [Member]	Jun. 30, 2012 Tender Offer Repurchases [Member]	Mar. 29, 2012 Tender Offer Repurchases [Member]	Jun. 30, 2012 Senior Unsecured Debt Repurchases [Member]	Jun. 30, 2012 Senior Unsecured Debt Repurchases [Member] 2028 Notes [Member]
Indebtedness (Textual) [Abstract]
Amount of notes paid off and retired at maturity					$ 61,829
Maximum aggregate cash tender offer price								100,000
Gain/Loss on retirement of debt	(6,223)	(3,233)	(6,222)	(4,099)			6,223		1
Purchase price senior unsecured notes			89,328			57,041	88,922			406
Principal amount repurchased			87,355			55,955	86,925			430
Unamortized debt issue discount							578		0
Unamortized loan commitment and origination fee							609		3
Unamortized settlement amount of interest rate protection agreements							2,599		20
Professional Service Fee							440
Indebtedness (Additional Textual) [Abstract]
Carrying value of industrial properties held under mortgage and other loan	765,195		765,195
Letter of credit, amount	$ 537		$ 537