New Accounting Standards (Narrative) (Details) - USD ($) $ in Thousands		3 Months Ended	6 Months Ended		12 Months Ended
	Jan. 01, 2018	Jun. 30, 2018	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
New Accounting Standards [Abstract]
Sales incentives					$ 16,000
Capitalized contract costs	$ 16,296	$ 16,300	$ 16,300
Capitalized Contract Cost, Amortization		4,480	8,595
Change in net cash provided by used in investing activities			42,623	$ 4,457
Cumulative effect adjustment from adoption of new accounting pronouncement	13,243	13,243	13,243
Deferred tax liability	4,058	$ 718,627	$ 718,627		690,767
New accounting standards, effect of change in revenue	$ 1,005
Provisional Transition Tax obligation					$ 1,000