Commitments and Contingencies Legal Liabilities (Details) - USD ($) $ in Millions	36 Months Ended
Dec. 31, 2017	Mar. 31, 2018
Other Liabilities Disclosure [Abstract]
Charges related to stucco-related claims	$ 28.4
Estimated Repair Costs for Affected Homes		$ 7.9
Amount Reserved for Legal Expenses	$ 0.4	$ 0.3

Amount of increase (decrease) in the standard and extended product warranty liability.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=68068213&loc=d3e12565-110249

Name:	us-gaap_ProductWarrantyAccrualPeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration