Senior Unsecured Notes and Secured Debt (Details 1) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Dec. 31, 2012
Unsecured note issuances
Senior unsecured debt issued	$ 0	$ 497,862,000
Senior unsecured debt redeemed	(1,000)	0
Excluding Fair Value Adjustments [Member]
Unsecured note issuances
Senior unsecured debt balance	7,418,374,000	6,640,127,000	7,421,707,000	6,145,457,000
Senior unsecured debt issued	0	500,000,000
Senior unsecured debt redeemed	(1,000)	0
Senior unsecured debt foreign currency	$ (3,332,000)	$ (5,330,000)
Senior unsecured debt balance average rate	0.044	0.044	0.044	0.046
Senior unsecured debt issued average rate	0	0.01552
Senior unsecured debt redeemed average rate	0.03	0
Senior unsecured debt foreign currency average rate	0.03486	0.0267