Acquisitions - Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Goodwill	$ 420,351		$ 401,758
Altek
Business Acquisition [Line Items]
Cash and cash equivalents	1,700	$ 1,700
Net working capital	(1,300)	(1,500)
Property, plant and equipment	3,300	3,300
Intangible assets	52,700	52,500
Goodwill	26,700	20,900
Net deferred tax liabilities	(8,500)	(8,500)
Other liabilities	(300)	(300)
Total identifiable net assets of Altek	74,300	$ 68,100
Measurement Period Adjustments
Net working capital	200
Intangible assets	200
Goodwill	5,800
Total identifiable net assets of Altek	$ 6,200