Subsequent Events	6 Months Ended
Jun. 30, 2019
Subsequent Events [Abstract]
Subsequent Events [Text Block]	13. Subsequent Events On July 16, 2019, the Company executed a 75-year ground lease with The George Washington University for land parcels at 2100 Pennsylvania Avenue located in Washington, DC and commenced development of an approximately 480,000 net rentable square foot Class A office property pursuant to a development agreement that the Company entered into with The George Washington University in 2016. The development agreement provided for the execution of the ground lease upon completion of the entitlement process and relocation of existing tenants. Also in 2016, the Company made a deposit of $15.0 million that, upon execution of the ground lease, will be credited against ground rent payable under the ground lease. In 2017, the Company entered into a 16-year lease with a tenant for approximately 300,000 net rentable square feet of space at the property.

The entire disclosure for significant events or transactions that occurred after the balance sheet date through the date the financial statements were issued or the date the financial statements were available to be issued. Examples include: the sale of a capital stock issue, purchase of a business, settlement of litigation, catastrophic loss, significant foreign exchange rate changes, loans to insiders or affiliates, and transactions not in the ordinary course of business.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 855
-URI http://asc.fasb.org/topic&trid=2122774

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