Supplemental Consolidated Balance Sheet Information (Components of Other Current Liabilities) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Balance Sheet Related Disclosures [Abstract]
Deferred acquisition liabilities - current	$ 978	$ 969
Contract liabilities	21,301	28,909
Deferred rent - current		2,656
Other current liabilities	482	1,510
Total other current liabilities	$ 22,761	$ 34,044