Investment Debt (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014 Loan		Dec. 31, 2013
Debt Instrument [Line Items]
Long-term debt	$ 1,628.3		$ 850.8
Number of loans	7
Ireland [Member]
Debt Instrument [Line Items]
Number of buildings acquired through change in control	3
Number of buildings acquired	2
Mortgage Loans and Notes Payable [Member]
Debt Instrument [Line Items]
Long-term debt	882.2
Debt unamortized premium	12.9
Mortgage Loans Payable [Member]
Debt Instrument [Line Items]
Long-term debt	882.2	[1]	401.8	[1]
Debt unamortized premium	12.9		5.3
Weighted average interest rate	4.35%		4.13%
Mortgage Loans Payable [Member] | Mortgage Loans Secured by Multi-Family Properties [Member] | Western United States [Member]
Debt Instrument [Line Items]
Long-term debt	260.2	[2]	261.0	[2]
Mortgage Loans Payable [Member] | Mortgage Loans Secured by Multi-Family Properties [Member] | Ireland [Member]
Debt Instrument [Line Items]
Long-term debt	202.8	[2]	0	[2]
Mortgage Loans Payable [Member] | Mortgage Loans Secured by Commerical Buildings [Member] | Western United States [Member]
Debt Instrument [Line Items]
Long-term debt	128.2		110.4
Mortgage Loans Payable [Member] | Mortgage Loans Secured by Commerical Buildings [Member] | Japan [Member]
Debt Instrument [Line Items]
Long-term debt	2.4		2.4
Mortgage Loans Payable [Member] | Mortgage Loans Secured by Commerical Buildings [Member] | Ireland [Member]
Debt Instrument [Line Items]
Long-term debt	75.2	[2]	0	[2]
Mortgage Loans Payable [Member] | Mortgage Loans Secured by Commerical Buildings [Member] | United Kingdom [Member]
Debt Instrument [Line Items]
Long-term debt	94.9	[2]	0	[2]
Mortgage Loans Payable [Member] | Mortgage Loans Secured by Residential Buildings [Member] | Western United States [Member]
Debt Instrument [Line Items]
Long-term debt	30.0		28.0
Mortgage Loans Payable [Member] | Mortgage Loans Secured by Notes Receivable [Member] | Ireland [Member]
Debt Instrument [Line Items]
Long-term debt	82.5	[2]	0	[2]
Mortgage Loans Payable [Member] | Mortgage Loans Secured by Notes Receivable [Member] | United Kingdom [Member]
Debt Instrument [Line Items]
Long-term debt	$ 6.0	[2]	$ 0	[2]

[1] The investment debt had a weighted average interest rate of 4.35% and 4.13% at March 31, 2014 and December 31, 2013.

[2] The investment debt balances include the unamortized debt premiums. Debt premiums represent the excess of the fair value of debt over the principal value of debt assumed in various acquisitions and are amortized into interest expense over the remaining term of the related debt in a manner that approximates the effective interest method. The unamortized loan premium as of March 31, 2014 and December 31, 2013 was $12.9 million and $5.3 million, respectively.