Contingencies Details (Details)	12 Months Ended
	Dec. 31, 2017
Former Davey employee defendants [Member]
Loss contingency, number of defendants	1
Wolf employee defendants [Member]
Loss contingency, number of defendants	2
Former Wolf employee defendants [Member]
Loss contingency, number of defendants	1
Defendants for which Davey has retained separate counsel [Member]
Loss contingency, number of defendants	3