Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ 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, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Net income attributable to the Company													$ 82,891	$ 33,111	$ 52,733
Weighted average number of shares used in calculating basic net income per share													32,252	32,169	32,086
Stock options													15	30	39
Long-term incentive plan													28	45	45
Weighted average number of shares used in calculating diluted net income per share													32,295	32,244	32,170
Average market price of common stock used for calculation of dilutive shares													$ 66.95	$ 52.19	$ 40.25
Basic	$ 0.54	$ 0.86	$ 0.93	$ 0.24	$ 0.19	$ 0.47	$ 0.03	$ 0.34	$ 0.49	$ 0.41	$ 0.32	$ 0.42	2.57	1.03	1.64
Diluted	$ 0.54	$ 0.86	$ 0.93	$ 0.24	$ 0.19	$ 0.47	$ 0.03	$ 0.34	$ 0.49	$ 0.41	$ 0.32	$ 0.42	$ 2.57	$ 1.03	$ 1.64
Common Stock, shares outstanding	32,300				32,200				32,100				32,300	32,200	32,100