Revenue Recognition (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Revenue Recognition [Line Items]
Contract liabilities	$ 21,301	$ 28,909
Remaining performance obligations expected to be satisfied beyond one year	$ 147,300
Contract termination notice days with no penality	30 days
Effect of Adoption of Topic 606 [Member]
Revenue Recognition [Line Items]
Contract liabilities	$ 21,300	$ 28,900
Amount of contract liability, revenue recognized	$ 17,700