Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended												12 Months Ended
	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, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net income attributable to the Company													$ 33,111	$ 52,733	$ 57,279
Weighted average number of shares used in calculating basic net income per share													32,169	32,086	31,978
Stock options													30	39	58
Long-term incentive plan													45	45	52
Weighted average number of shares used in calculating diluted net income per share													32,244	32,170	32,088
Average market price of common stock used for calculation of dilutive shares													$ 52.19	$ 40.25	$ 36.68
Basic	$ 0.19	$ 0.47	$ 0.03	$ 0.34	$ 0.49	$ 0.41	$ 0.32	$ 0.42	$ 1.18	$ 0.30	$ (0.07)	$ 0.38	1.03	1.64	1.79
Diluted	$ 0.19	$ 0.47	$ 0.03	$ 0.34	$ 0.49	$ 0.41	$ 0.32	$ 0.42	$ 1.18	$ 0.30	$ (0.07)	$ 0.38	$ 1.03	$ 1.64	$ 1.79
Common Stock, shares outstanding	32,200				32,100				32,000				32,200	32,100	32,000