Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net income attributable to the Company	$ 28,215	$ 15,269	$ 68,825	$ 27,225
Weighted average number of shares:
Weighted average number of shares used in calculating basic net income per share	32,264	32,187	32,247	32,160
Effect of dilutive stock-based compensation plans:
Stock options	16	27	16	33
Weighted average number of shares used in calculating diluted net income per share	32,280	32,214	32,263	32,193
Average market price of common stock used for calculation of dilutive shares	$ 72.30	$ 53.49	$ 66.01	$ 49.49
Net income attributable to the Company per share:
Basic	0.87	0.47	2.13	0.85
Diluted	$ 0.87	$ 0.47	$ 2.13	$ 0.85