Other intangible assets (Details 2) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Intangible assets, net (excluding goodwill)	$ 11,680,000	$ 3,465,000	$ 10,815,000
Amortization of intangible assets	600,000	400,000
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	14,471,000	14,668,000	22,720,000
Intangible assets, less accumulated amortization	5,156,000	13,007,000	13,535,000
Intangible assets, net (excluding goodwill)	9,315,000	1,661,000	9,185,000
Noncompete agreements
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	3,179,000	2,430,000	2,605,000
Intangible assets, less accumulated amortization	1,730,000	1,842,000	1,956,000
Intangible assets, net (excluding goodwill)	1,449,000	588,000	649,000
Other intangible assets
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	6,458,000	6,458,000	6,458,000
Intangible assets, less accumulated amortization	5,542,000	5,242,000	5,477,000
Intangible assets, net (excluding goodwill)	916,000	$ 1,216,000	$ 981,000
Construction materials and contracting [Member] | Series of Individually Immaterial Business Acquisitions [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 1,500,000