COPT Defense Properties Annual report pursuant to Section 13 and 15(d)

Information by Business Segment (Details 3) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reconciliation of segment assets to total assets
Assets	$ 3,670,257us-gaap_Assets	$ 3,629,952us-gaap_Assets
Segment assets
Reconciliation of segment assets to total assets
Assets	2,951,495	2,905,630	2,945,930
Non-operating property assets
Reconciliation of segment assets to total assets
Assets	567,586	517,564
Other assets
Reconciliation of segment assets to total assets
Assets	$ 151,176	$ 206,758