Commitments and Contingencies (Details) ft² in Thousands	May 04, 2016 USD ($) a ft²	Jan. 25, 2016 USD ($) a	Nov. 30, 2016 USD ($)	Mar. 23, 2016 a
Commitments and Contingencies
Stock repurchase program, authorized amount			$ 5,000,000
Common stock repurchase program, remaining authorized amount			1,646,000
Agreement to sell
Commitments and Contingencies
Agreement Term of Extension		3 years
Number of acres to be sold | a		280
Sale price		$ 7,700,000
Obligations For Investments In Real Estate Assets [Member]
Commitments and Contingencies
Purchase obligations			$ 1,677,000
East Allen Township Northampton County PA Site [Member] | Obligations For Investments In Real Estate Assets [Member] | Purchase agreement
Commitments and Contingencies
Number of acres | a				31
Upper Macungie Township Lehigh County PA Site [Member] | Obligations For Investments In Real Estate Assets [Member]
Commitments and Contingencies
Area Of Building | ft²	134
Upper Macungie Township Lehigh County PA Site [Member] | Obligations For Investments In Real Estate Assets [Member] | Purchase agreement
Commitments and Contingencies
Purchase obligations	$ 1,800,000
Number of acres | a	14