Marketable Securities and Derivative Instruments: Derivative Instruments (Narratives) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	9 Months Ended		3 Months Ended	0 Months Ended		3 Months Ended							0 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 Other Investments [Member]	Sep. 19, 2013 JC Penney [Member]	Mar. 04, 2013 JC Penney [Member]	Mar. 31, 2013 JC Penney [Member]	Sep. 30, 2013 JC Penney [Member]	Sep. 30, 2013 Lexington Realty Trust [Member] Minimum [Member]	Mar. 31, 2013 Lexington Realty Trust [Member] Maximum [Member]	Mar. 31, 2013 Shares Owned [Member] JC Penney [Member]	Dec. 31, 2012 Shares Owned [Member] JC Penney [Member]	Dec. 31, 2012 Forward Contracts [Member] JC Penney [Member]	Sep. 19, 2013 Common Shares [Member] JC Penney [Member]	Dec. 31, 2012 Common Shares [Member] JC Penney [Member]
Derivative [Line Items]
Ownership Percentage								8.80%	17.20%
Number of shares owned										8,584,010	23,400,000	4,815,990		18,584,010
Investment Owned, at Cost											$ 366,291	$ 141,309
Strike price of common shares held under forward contract (in dollars per share)												$ 29.34
Sale of Stock, Number of Shares				13,400,000	10,000,000
Sale price, per share (in dollars per share)				$ 13.00	$ 16.03
Proceeds From Sale Of JC Penney Common Shares				174,200	160,300
Net loss on sale of common shares in J.C Penney			31,741	(18,114)	(36,800)
Closing share price (in dollars per share)						$ 15.11					$ 19.71
Non-cash impairment loss on J.C. Penney common shares	39,487	0				39,487
Receipt of common shares by settling forward contract													4,815,990
Unrealized Gain Loss On Derivatives	(33,487)	(53,343)											(20,012)
Proceeds from sales of marketable securities	378,676	58,460	44,176
Net economic gain or (loss) on investment in marketable securities							$ (256,156)