Accounting Policies - Earnings Per Share Anti-Dilutive (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net Income (Loss) Available to Common Stockholders, Basic	$ 12,006	$ 22,162	$ 22,323	$ 23,980
Net Income (Loss) Available to Common Stockholders, Diluted	$ 12,006	$ 22,162	$ 22,323	$ 23,980
Stock options, SARs and restricted stock	158,000	428,000	348,000	411,000
Weighted Average Number of Shares Outstanding, Basic	10,456,000	11,010,000	10,460,000	10,974,000
Basic earnings per common share	$ 1.15	$ 2.01	$ 2.13	$ 2.19
Earnings Per Share, On Incremental Common Shares Attributable to Share-based Payment Arrangements	$ (0.02)	$ (0.07)	$ (0.06)	$ (0.08)
Weighted Average Number of Shares Outstanding, Diluted	10,614,000	11,438,000	10,808,000	11,385,000
Diluted earnings per common share	$ 1.13000	$ 1.94000	$ 2.07000	$ 2.11000
Stock Options and SARs [Members]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from earnings per share (shares)	82,052	229,693	146,458.50	215,547
Performance Shares [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from earnings per share (shares)	37,284	45,034	37,284	37,774