Secured and unsecured senior debt Schedule of changes made to long-term debts (Details) (USD $) In Thousands, unless otherwise specified		0 Months Ended	1 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended		1 Months Ended		7 Months Ended	12 Months Ended
	Dec. 31, 2013	Jul. 26, 2013 2016 Unsecured Senior Bank Term Loan	Aug. 30, 2013 2016 Unsecured Senior Bank Term Loan	Dec. 31, 2013 2016 Unsecured Senior Bank Term Loan	Aug. 30, 2013 2019 Unsecured Senior Bank Term Loan	Dec. 31, 2013 2019 Unsecured Senior Bank Term Loan	Jul. 31, 2013 2019 Unsecured Senior Bank Term Loan	Aug. 30, 2013 Line of Credit	Apr. 30, 2012 Line of Credit	Jul. 31, 2013 Line of Credit	Dec. 31, 2013 Line of Credit		Dec. 31, 2013 Secured notes payable maturing on 7/1/15 Extension_Option
Debt Instrument [Line Items]
Principal amount	$ 3,061,061			$ 500,000		$ 600,000					$ 204,000
Basis spread on LIBOR (as a percent)		1.75%		1.20%		1.20%	1.50%			1.20%	1.10%	[1]	1.50%
Number of one-year extension options													2
Annual facility fee (as a percent)								0.20%	0.20%	0.25%	0.20%
Base rate		LIBOR	LIBOR	LIBOR	LIBOR	LIBOR		LIBOR		LIBOR	LIBOR	[1]	LIBOR

[1] In addition to the stated rate, the line of credit is subject to an annual facility fee of 0.20%.