Cash Flow Information (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Real Estate Properties
Deferred acquisition fees payable (Note 3, 4)	$ 3,183	$ 14,472	$ 17,394
Reclassification to Assets held for sale	13,166	0	0
Build-to-suit construction costs incurred but unpaid	0	0	1,112
Conversion of note receivable to equity investment in real estate (Note 6)	2,047	0	0
Asset retirement obligations (Note 4)	1,619	6,842	9,562
Non-recourse mortgage loans assumed on acquisition (Note 11)	0	36,747	273,074
Fourth quarter distributions declared	51,570	46,412	32,288
In-place lease
Real Estate Properties
Reclassification to real estate	548	(1,579)	0
Reclassification from real estate	0	0	0
Real estate
Real Estate Properties
Reclassification to real estate	38,945	142,085	69,368
Reclassification from real estate	(9,825)	(7,378)	0
Operating real estate
Real Estate Properties
Reclassification to real estate	12,557	0	0
Reclassification from real estate	(13,166)	0	0
Real estate under construction
Real Estate Properties
Reclassification from real estate	(42,225)	(142,085)	(69,368)
Net investment in direct financing leases
Real Estate Properties
Reclassification to real estate	0	8,957	0
Equity method investments
Real Estate Properties
Hellweg 2 purchase option (Note 6)	$ 0	$ 32,338	$ 0