Background (Details)	12 Months Ended
	Dec. 31, 2013 Lease Tenant property sqft
Nature of Business [Line Items]
Number of properties	180
Total rentable area (in square feet)	17,461,030
Number of leases held	527
Number of client tenants	425
Number of single-tenant properties	79
Single-tenant properties as a percentage of total properties	44.00%
Investment-grade client tenants as a percentage of total annualized base rent	51.00%
Percentage of leases which are triple net leases	94.00%
Percentage of leases containing effective annual rent escalations	95.00%
Percentage of leases providing for recapture of certain capital expenditures	92.00%
Minimum
Nature of Business [Line Items]
Lease term of multi-tenant buildings	4 years
Lease term of single-tenant buildings	8 years
Effective annual rent escalations (as a percent)	3.00%
Maximum
Nature of Business [Line Items]
Lease term of multi-tenant buildings	11 years
Lease term of single-tenant buildings	17 years
Effective annual rent escalations (as a percent)	3.50%