Segments Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation From Segment Totals To Consolidated Abstract
Operating income for reportable segments	$ 184,183				$ 165,313				$ 184,183	$ 165,313	$ 158,895
Non-operating Charges									(72,223)	(65,142)	(65,316)
Restructuring and related activities									0	0	439
Combination-related expenses									(16,661)	(29,938)	(1,531)
Depreciation of corporate assets and amortization									(7,518)	(7,489)	(7,134)
Operating income	$ 20,068	$ 24,919	$ 22,563	$ 20,231	$ 17,074	$ 14,009	$ 17,903	$ 13,758	87,781	62,744	85,353
Interest expense									(6,158)	(3,892)	(2,889)
Interest income									2,117	2,534	2,037
Other expense, net									(642)	(718)	(492)
Income before taxes and equity in net income of associated companies									$ 83,098	$ 60,668	$ 84,009