Revenue (Disaggregation of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue
Disaggregated sales	$ 2,314,957	$ 2,482,717	$ 2,456,073	$ 2,282,681	$ 2,190,808	$ 2,339,830	$ 2,290,829	$ 2,156,259	$ 9,536,428	$ 8,977,726	$ 8,593,096
DIY customer [Member]
Disaggregation of Revenue
Disaggregated sales									5,351,035	5,113,288	4,911,826
Professional service provider customer [Member]
Disaggregation of Revenue
Disaggregated sales									4,035,898	3,724,220	3,540,116
Other customers and sales adjustments [Member]
Disaggregation of Revenue
Disaggregated sales									$ 149,495	$ 140,218	$ 141,154