Investments in Real Estate and Real Estate Under Construction Summary of acquisitions and build-to-suit transactions (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014
Investments in Real Estate and Real Estate Under Construction [Line Items]
Initial cost basis	$ 141,880
Land and land estate	7,722
Building and improvements	112,686
Lease in-place value	21,472
Industrial property [Member] | Rantoul, Illinois [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Initial cost basis	41,277
Land and land estate	1,304
Building and improvements	32,562
Lease in-place value	7,411
Industrial property [Member] | Lewisburg, Tennessee [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Initial cost basis	13,320
Land and land estate	173
Building and improvements	10,865
Lease in-place value	2,282
Industrial property [Member] | North Las Vegas, Nevada [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Initial cost basis	28,249
Land and land estate	3,244
Building and improvements	21,444
Lease in-place value	3,561
Industrial property [Member] | Bingen, Washington [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Initial cost basis	20,391
Land and land estate	0
Building and improvements	18,075
Lease in-place value	2,316
Office Building [Member] | Parachute, Colorado [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Initial cost basis	13,928
Land and land estate	1,400
Building and improvements	10,751
Lease in-place value	1,777
Office Building [Member] | Rock Hill, South Carolina [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Initial cost basis	24,715
Land and land estate	1,601
Building and improvements	18,989
Lease in-place value	$ 4,125