Senior Unsecured Notes and Secured Debt (Details 1) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013
Unsecured note issuances
Senior unsecured debt issued	$ 0	$ 0
Senior unsecured debt redeemed	(154,654,000)	(1,000)
Excluding Fair Value Adjustments [Member]
Unsecured note issuances
Senior unsecured debt balance	7,567,921,000	7,418,374,000	7,817,154,000	7,421,707,000
Senior unsecured debt issued	0	0
Senior unsecured debt extinguished	0
Senior unsecured debt redeemed	(154,654,000)	(1,000)
Senior unsecured debt foreign currency	$ (94,579,000)	$ (3,332,000)
Senior unsecured debt balance average rate	0.04352	0.044	0.04385	0.044
Senior unsecured debt issued average rate	0	0
Senior unsecured debt extinguished average rate	0	0
Senior unsecured debt redeemed average rate	0.03	0.03
Senior unsecured debt foreign currency average rate	0.04333	0.03486