Revenues - Contract Asset and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Revenue Recognition [Abstract]
Short-term unbilled receivables - included in accounts receivable and unbilled receivables	$ 15,524	$ 9,191
Other long-term assets	12,794	16,481
Total contract assets	28,318	25,672
Deferred revenues, net	88,205	81,835
Long-term deferred revenues	7,979	10,582
Total contract liabilities	$ 96,184	$ 92,417