Variable Interest Entities (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012 Consolidated Variable Interest Entities [Member] Independance Plaza [Member]	Dec. 31, 2012 Non Consolidated Variable Interest Entities [Member] Washington DC Office Warner Building [Member]	Dec. 31, 2013 Non Consolidated Variable Interest Entities [Member] Independence Plaza And Warner Building [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	$ 957,730
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	443,894
Variable Interest Entity Consolidated Carrying Amount Noncontrolling Interest	193,933
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets		$ 8,775	$ 152,929