Subsequent Events (Details) (USD $) In Thousands, unless otherwise specified	0 Months Ended
	Dec. 31, 2014 subsidiary	Nov. 30, 2014 sqft	Nov. 30, 2013
Subsequent events
Mortgage loans		$ 70,168	$ 66,708
Area of collateralized properties (in square feet)		280,000
Subsequent events | 2025 First Niagara Mortgage
Subsequent events
Number of subsidiaries which are refinancing norerecourse mortgage loan	2
Mortgage loans	$ 21,600
Term of debt	10 years
Subsequent events | 2025 First Niagara Mortgage | Lower Nazareth, Pennsylvania | Location 1
Subsequent events
Area of collateralized properties (in square feet)	228,000
Subsequent events | 2025 First Niagara Mortgage | Lower Nazareth, Pennsylvania | Location 2
Subsequent events
Area of collateralized properties (in square feet)	303,000