Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Net income attributable to the Company	$ 30,365	$ 1,117	$ 40,610	$ 11,956
Weighted average number of shares:
Weighted average number of shares used in calculating basic net income per share	32,257	32,166	32,239	32,147
Effect of dilutive stock-based compensation plans:
Stock options	16	34	16	35
Weighted average number of shares used in calculating diluted net income per share	32,273	32,200	32,255	32,182
Average market price of common stock used for calculation of dilutive shares	$ 61.86	$ 48.44	$ 62.83	$ 47.47
Net income per share:
Basic	0.94	0.03	1.26	0.37
Diluted	$ 0.94	$ 0.03	$ 1.26	$ 0.37