Marketable Securities and Derivative Instruments: Derivative Instruments (Narratives) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	6 Months Ended		0 Months Ended	3 Months Ended						3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Mar. 04, 2013 JC Penney [Member]	Mar. 31, 2013 JC Penney [Member]	Jun. 30, 2013 JC Penney [Member]	Dec. 31, 2012 JC Penney [Member]	Jun. 30, 2013 Lexington Realty Trust [Member] Minimum [Member]	Jun. 30, 2013 Lexington Realty Trust [Member] Maximum [Member]	Jun. 30, 2013 Shares Owned [Member] JC Penney [Member]	Jun. 30, 2013 Forward Contracts [Member] JC Penney [Member]	Jun. 30, 2012 Forward Contracts [Member] JC Penney [Member]	Jun. 30, 2013 Forward Contracts [Member] JC Penney [Member]	Jun. 30, 2012 Forward Contracts [Member] JC Penney [Member]
Derivative [Line Items]
Sale of Stock, Number of Shares			10,000,000
Sale price, per share (in dollars per share)			$ 16.03
Proceeds From Sale Of JC Penney Common Shares			$ 160,300
Net loss on sale of common shares in J.C Penney			(36,800)
Number of shares owned					13,400,000				8,584,010	4,815,990		4,815,990
Ownership Percentage					6.10%		8.80%	17.20%
Investment Owned, at Cost									129,704
Closing share price (in dollars per share)					$ 17.08	$ 15.11
Investment Owned At Fair Value									146,615
Non-cash impairment loss on J.C. Penney common shares	39,487	0		39,487
Strike price of common shares held under forward contract (in dollars per share)										$ 29.27		$ 29.27
Notional Amount Of Price Risk Derivatives										140,947		140,947
Derivative Maturity Date												Oct. 08, 2022
Funding Related To Derivative Position												69,377
Percentage Increase In Forward Contract Strike Price For First Two Years										0.95%		0.95%
Percentage Increase In Forward Contract Strike Price For Third Year Onward										0.80%		0.80%
Description Of Basis Spread For Increase In Strike Price										LIBOR		LIBOR
Derivative Gain On Derivative	(13,475)	(57,687)								9,065	(58,732)	(13,475)	(57,687)
Net economic gain or (loss) on investment in marketable securities					$ 201,119