Marketable Securities and Derivative Instruments: Marketable Securities (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair value	$ 205,042	$ 191,917
Available-for-sale Equity Securities, Amortized Cost Basis	72,608	72,608
Available-for-sale Securities, Gross Unrealized Gain (Loss)	132,434	119,309
Lexington Realty Trust [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair value	201,496	188,567
Available-for-sale Equity Securities, Amortized Cost Basis	72,549	72,549
Available-for-sale Securities, Gross Unrealized Gain (Loss)	128,947	116,018
Other Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair value	3,546	3,350
Available-for-sale Equity Securities, Amortized Cost Basis	59	59
Available-for-sale Securities, Gross Unrealized Gain (Loss)	$ 3,487	$ 3,291