Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(14))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(8))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(13))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_PropertyPlantAndEquipmentNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Subsequent Events (Details) $ / shares in Units, $ in Millions		1 Months Ended	3 Months Ended		6 Months Ended
	Aug. 06, 2019 $ / shares	Jul. 31, 2019 USD ($)	Jun. 30, 2019 USD ($) ft² $ / shares	Jun. 30, 2018 $ / shares	Jun. 30, 2019 USD ($) ft² $ / shares	Jun. 30, 2018 $ / shares
Subsequent Event [Line Items]
Common Stock, Dividends, Per Share, Declared \| $ / shares			$ 0.225	$ 0.225	$ 0.225	$ 0.225
Subsequent Event [Member]
Subsequent Event [Line Items]
Common Stock, Dividends, Per Share, Declared \| $ / shares	$ 0.225
1600 K Street [Member] \| Washington, D.C. [Member] \| Commercial Segment [Member]
Subsequent Event [Line Items]
Area of real estate property (in square feet) \| ft²			83,000		83,000
Property, Plant and Equipment, Net \| $			$ 32.9		$ 32.9
1600 K Street [Member] \| Washington, D.C. [Member] \| Commercial Segment [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Proceeds from Sale of Property Held-for-sale \| $		$ 43.0