Acquisition and Divestiture Activities (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Acquisition of business, net of cash acquired		$ 0	$ 0	$ 6,750
Acquisition of noncontrolling interests		(4,100)	0	0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Goodwill		$ 142,742	141,407	138,244
UltraSource [Member]
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Acquisition of business, net of cash acquired	$ 13,372
Business Acquisition, Name of Acquired Entity	Ultrasource, Inc.
Business Acquisition, Effective Date of Acquisition	Feb. 08, 2018
Sonntag [Member]
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Acquisition of business, net of cash acquired			5,450
Goodwill related to acquisitions			$ 3,485
Gross purchase price of acquired business				$ 6,750
Business Acquisition, Name of Acquired Entity			Sonntag Electronic GmbH
Business Acquisition, Effective Date of Acquisition			Jan. 01, 2016