Revenue Recognition (Receivables and Deferred Revenue) (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($)
Contract Balances [Roll Forward]
Opening balance, Receivable	$ 37,926
Ending balance, Receivable	38,109
Opening balance, Deferred Revenue (current)	35,563
Increase (decrease) in current deferred revenue, net	11,812
Ending balance, Deferred Revenue (current)	47,375
Opening balance, Deferred Revenue (long-term)	0
Increase (decrease) in long-term deferred revenue, net	2,131
Ending balance, Deferred Revenue (long-term)	2,131
Accounts Receivable
Contract Balances [Roll Forward]
Opening balance, Receivable	30,342
Increase (decrease) in accounts receivable, net	(640)
Ending balance, Receivable	29,702
Unbilled Receivable
Contract Balances [Roll Forward]
Opening balance, Receivable	7,584
Increase (decrease) in unbilled receivables, net	823
Ending balance, Receivable	$ 8,407