Revenue (Narrative) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Revenue from Contracts with Customer [Line Items]
Accounts receivable, net	$ 331,239	$ 337,927
Contract assets	9,400	7,400
Contract liabilities	2,300	$ 1,700
Revenue recognized from contract liability during the period	$ 1,700
Average transit time	3 days