Business Combination Business Combination (Details) (USD $)	3 Months Ended								12 Months Ended			0 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Oct. 08, 2013 sqft
Business Combination, Costs Incurred or to be Incurred [Abstract]
Deferred financing costs	$ 38,445,000				$ 36,883,000				$ 38,445,000	$ 36,883,000
Proceeds from unsecured notes									0	448,646,000	700,000,000
Business Acquisition, Pro Forma Information [Abstract]
Operating revenue	203,685,000	198,356,000	192,960,000	197,630,000	192,427,000	155,349,000	151,026,000	147,128,000	792,631,000	645,930,000	560,279,000
Operating Income (Loss)									257,423,000	203,047,000	189,942,000
Senior Notes [Member] | 4.40% senior unsecured note [Member]
Business Combination, Costs Incurred or to be Incurred [Abstract]
Proceeds from unsecured notes										450,000,000
Common Stock [Member]
Business Combination, Costs Incurred or to be Incurred [Abstract]
Number of common shares issued									0	1,900,000	0
Common Shares Equity Offering [Member] | Common Stock [Member]
Business Combination, Costs Incurred or to be Incurred [Abstract]
Number of common shares issued										24,200,000
Cabot Industrial Value Fund III [Member]
Business Combination, Description [Abstract]
Name of Acquired Entity										Cabot Industrial Fund III Operating Partnership, L.P.
Percentage of Voting Interests Acquired												100.00%
Square Footage of Real Estate Property												23,000,000
Business Acquisition, Date of Acquisition [Abstract]
Date of Acquisition									Oct. 08, 2013
Business Combination, Consideration Transferred [Abstract]
Total purchase price of acquisition												1,469,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets [Abstract]
Land and land improvements												247,393,000
Building and improvements												1,152,717,000
Operating real estate												1,400,110,000
Intangible - in-place leases/market rent												97,396,000
Other assets												4,953,000
Total assets												1,502,459,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities [Abstract]
Mortgage loans					243,200,000					243,200,000		243,230,000
Other liabilities												32,958,000
Intangible market rent												5,737,000
Total liabilities												281,925,000
Net assets acquired												1,220,534,000
Business Combination, Costs Incurred or to be Incurred [Abstract]
Acquisition costs										7,600,000
Financing fees										4,200,000
Deferred financing costs					2,000,000					2,000,000
Mortgage loans acquired before fair value adjustment					229,800,000					229,800,000
Stock issuance costs										35,300,000
Business Acquisition, Pro Forma Information [Abstract]
Total operating revenue										750,896,000	692,583,000
Net income available to common shareholders										211,601,000	134,295,000
Operating revenue										31,400,000
Operating Income (Loss)										22,000,000
Cabot Industrial Value Fund III [Member] | Mortgages [Member]
Business Combination, Consideration Transferred [Abstract]
Assumption of mortgage debt from acquisition												229,800,000
Cabot Industrial Value Fund III [Member] | Senior Notes [Member] | 4.40% senior unsecured note [Member]
Business Combination, Costs Incurred or to be Incurred [Abstract]
Deferred financing costs					$ 3,900,000					$ 3,900,000
Cabot Industrial Value Fund III [Member] | Leases, Acquired-in-Place [Member]
Acquired Finite-Lived Intangible Assets [Abstract]
Weighted average useful life of acquired of in-place lease intangible assets										4 years 5 months 0 days
Industrial Property [Member] | Cabot Industrial Value Fund III [Member]
Business Combination, Description [Abstract]
Number of Real Estate Properties												177