Accounting Policies - 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
Accounting Policies [Abstract]
Net income attributable to common stockholders (Dilutive)	$ 26,340	$ 17,488	$ 48,864	$ 36,103
Stock options, SARs and restricted stock	84	183	102	207
Earnings Per Share, On Incremental Common Shares Attributable to Share-based Payment Arrangements	$ (0.02)	$ (0.03)	$ (0.04)	$ (0.06)
Weighted Average Number of Shares Outstanding, Diluted	10,742	10,783	10,742	10,783
Diluted earnings per common share	$ 2.45000	$ 1.62000	$ 4.55000	$ 3.35
Earnings Per Share, Basic [Abstract]
Net Income (Loss) Available to Common Stockholders, Basic	$ 26,340	$ 17,488	$ 48,864	$ 36,103
Weighted Average Number of Shares Outstanding, Basic	10,658	10,600	10,640	10,576
Basic earnings per common share	$ 2.47	$ 1.65	$ 4.59	$ 3.41