Business Acquisition - Narrative (Details) - USD ($) $ in Thousands	Aug. 05, 2015	Sep. 30, 2015	Dec. 31, 2014	Dec. 31, 2013
Business Acquisition [Line Items]
Goodwill		$ 70,518	$ 33,798	$ 33,798
GLM Concrete Solutions, LLC
Business Acquisition [Line Items]
Issued and outstanding membership interest acquired	49.00%
TAS Commercial Concrete
Business Acquisition [Line Items]
Payments to acquire businesses	$ 112,000
Goodwill	36,720
Goodwill expected to be tax deductible	$ 36,700
Goodwill, tax basis, amortization period	15 years
Acquisition related costs	$ 400
TAS Commercial Concrete | Minimum
Business Acquisition [Line Items]
Property and equipment useful life	3 years
TAS Commercial Concrete | Maximum
Business Acquisition [Line Items]
Property and equipment useful life	15 years