Fair Value Measurements (Other Fair Value Disclosures) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Level 2 [Member] \| Senior Unsecured Notes [Member]
Other Fair Value Measurements
Senior unsecured notes	$ 959.9	$ 971.6

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=121572278&loc=d3e13433-108611

Name:	us-gaap_DebtInstrumentFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant