Inventories (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Inventory [Line Items]
Inventories	$ 20.7	$ 20.7
Asphalt
Inventory [Line Items]
Inventories	8.1	8.0
Processed rock and sand
Inventory [Line Items]
Inventories	6.2	6.6
Work in progress
Inventory [Line Items]
Inventories	3.1	2.9
Retail merchandise
Inventory [Line Items]
Inventories	2.0	2.0
Parts, materials and supplies inventories
Inventory [Line Items]
Inventories	$ 1.3	$ 1.2

Amount after valuation and LIFO reserves of inventory expected to be sold, or consumed within one year or operating cycle, if longer.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118951113&loc=d3e6676-107765

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 330
-SubTopic 10
-Section 35
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=116846819&loc=d3e3927-108312

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 210.5-02.6(a))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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