Income Taxes - Components of Expense and Earnings (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current Income Tax Expense (Benefit) [Abstract]
Federal	$ 21,265	$ 4,680	$ 8,924
State	2,529	518	188
Foreign	14,105	12,540	11,074
Current Income Tax Expense (Benefit), Total	37,899	17,738	20,186
Deferred Income Tax Expense (Benefit) [Abstract]
Federal	6,889	4,601	404
State	(36)	104	(16)
Foreign	(3,099)	783	(2,789)
Income Tax Expense (Benefit), Total	41,653	23,226	17,785
Components Of Earnings Before Taxes [Abstract]
Domestic	10,468	31,175	25,219
Foreign	50,200	52,834	45,011
Income before taxes and equity in net income of associated companies	$ 60,668	$ 84,009	$ 70,230