Accounting Policies - Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounting Policies [Abstract]
Net income attributable to common stockholders (Dilutive)									$ 47,371	$ 38,251	$ 71,833
Stock options, SARs and restricted stock									360	447	393
Earnings Per Share, On Incremental Common Shares Attributable to Share-based Payment Arrangements									$ (0.14)	$ (0.13)	$ (0.23)
Weighted Average Number of Shares Outstanding, Diluted									11,309	11,367	11,209
Diluted earnings per common share	$ 1.35	$ 0.74	$ 1.94	$ 0.16	$ 0.50	$ 1.02	$ 1.78	$ 0.07	$ 4.19000	$ 3.37000	$ 6.41000
Earnings Per Share, Basic [Abstract]
Weighted Average Number of Shares Outstanding, Basic									10,949	10,920	10,816
Basic earnings per common share	$ 1.39	$ 0.76	$ 2.01	$ 0.17	$ 0.52	$ 1.06	$ 1.85	$ 0.07	$ 4.33	$ 3.50	$ 6.64
Net Income (Loss) Available to Common Stockholders, Basic	$ 15,032	$ 8,359	$ 22,162	$ 1,818	$ 5,647	$ 11,586	$ 20,205	$ 813	$ 47,371	$ 38,251	$ 71,833