Goodwill and Intangible Assets - Narrative (Details) - USD ($) $ in Thousands		3 Months Ended	9 Months Ended		12 Months Ended
	Aug. 05, 2015	Sep. 30, 2015	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2012
Business Acquisition [Line Items]
Amortization expense			$ 1,733	$ 84
TAS Commercial Concrete
Business Acquisition [Line Items]
Business combination, indefinite-lived intangible assets	$ 6,900
Amortization expense		$ 1,700
TAS Commercial Concrete | Contractual backlog
Business Acquisition [Line Items]
Finite-lived intangibles acquired	$ 8,500
Acquired finite-lived intangible assets, useful life	2 years
TAS Commercial Concrete | Customer Relationships
Business Acquisition [Line Items]
Finite-lived intangibles acquired	$ 17,700
Acquired finite-lived intangible assets, useful life	8 years
West Construction, Inc.
Business Acquisition [Line Items]
Amortization expense		$ 87
West Construction, Inc. | Minimum
Business Acquisition [Line Items]
Acquired finite-lived intangible assets, useful life					1 year
West Construction, Inc. | Maximum
Business Acquisition [Line Items]
Acquired finite-lived intangible assets, useful life					3 years