Including the current and noncurrent portions, carrying value as of the balance sheet date of a type of municipal bond typically used to fund a development project. Also called special assessment limited liability bond, special district bond, special purpose bond, special tax bond and community development obligation. Interest owed to lenders is paid by taxes levied on the community benefiting from the particular bond-funded project. For example, if a bond of this sort was issued to pay for sidewalks to be repaved in a certain community, an additional tax would be levied on homeowners in the area benefiting from this project.

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(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: 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)(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 3: 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(19))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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

Contingencies - Litigation and Other Matters (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 Community	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)
Legal Reserve
Loss Contingencies [Line Items]
Accrued amounts for litigation and other contingent liabilities		$ 5.1	$ 5.0
Performance Bonds
Loss Contingencies [Line Items]
Letters of credit secured using cash collateral		37.4
Outstanding performance bonds		$ 257.3
CALIFORNIA
Loss Contingencies [Line Items]
Number of communities \| Community	15