Accounting Policies - 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
Accounting Policies [Abstract]
Net income attributable to common stockholders (Dilutive)	$ 26,474	$ 18,487	$ 75,338	$ 54,590
Stock options, SARs and restricted stock	76	210	93	208
Earnings Per Share, On Incremental Common Shares Attributable to Share-based Payment Arrangements	$ (0.02)	$ (0.03)	$ (0.06)	$ (0.10)
Weighted Average Number of Shares Outstanding, Diluted	10,744	10,815	10,743	10,794
Diluted earnings per common share	$ 2.46000	$ 1.71000	$ 7.01000	$ 5.06
Earnings Per Share, Basic [Abstract]
Net Income (Loss) Available to Common Stockholders, Basic	$ 26,474	$ 18,487	$ 75,338	$ 54,590
Weighted Average Number of Shares Outstanding, Basic	10,668	10,605	10,650	10,586
Basic earnings per common share	$ 2.48	$ 1.74	$ 7.07	$ 5.16