Intangible Assets - Cost and Net (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Intangible assets, net
Balance at cost	$ 78,506
Accumulated amortization	(40,618)
Ending Balance	37,888	$ 46,549	$ 37,970
Acquired Technology
Intangible assets, net
Balance at cost	37,294
Accumulated amortization	(30,348)
Ending Balance	6,946	11,392	34,632
Customer Relationships
Intangible assets, net
Balance at cost	27,831
Accumulated amortization	(5,287)
Ending Balance	22,544	24,774	828
Other
Intangible assets, net
Balance at cost	13,381
Accumulated amortization	(4,983)
Ending Balance	$ 8,398	$ 10,383	$ 2,510