Other Non-Operating Income (Details 1) - USD ($) $ in Thousands	3 Months Ended					12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Other Nonoperating Income (Expense) [Abstract]
Document Fiscal Year Focus	2018
Gain (loss) on sales of businesses	$ 5,907				$ (342)
Gain on sale of a cost method investment	2,845				0
Foreign currency gain, net	177				1,728
Other, net	258				(537)
Total Other Non-Operating Income	9,187	$ (2,640)	$ 1,963	$ 4,069	$ 849	$ 4,241	$ (12,642)
Gain on sales of marketable equity securities (see Note 2)	$ 28,500