Accounting Policies - Earnings Per Share Anti-Dilutive (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net Income (Loss) Available to Common Stockholders, Basic		$ 18,615	$ 10,317
Net Income (Loss) Available to Common Stockholders, Diluted		$ 18,615	$ 10,317
Stock options, SARs and restricted stock	[1]	231,000	538,000
Weighted Average Number of Shares Outstanding, Basic		10,551,000	10,465,000
Basic earnings per common share		$ 1.76	$ 0.99
Earnings Per Share, On Incremental Common Shares Attributable to Share-based Payment Arrangements	[1]	$ (0.03)	$ (0.05)
Weighted Average Number of Shares Outstanding, Diluted		10,782,000	11,003,000
Diluted earnings per common share		$ 1.73000	$ 0.94000
Stock Options and SARs [Members]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from earnings per share (shares)		50,757	201,401
Performance Shares [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from earnings per share (shares)		32,892	37,284

[1] For the three months ended March 31, 2017 and 2016, stock options and SARs of 50,757 and 201,401, respectively, were outstanding but not included in the computation of diluted earnings per share of common stock because they were anti-dilutive. For the three months ended March 31, 2017 and 2016, contingent shares of non-vested restricted stock of 32,892, and 37,284, respectively, were outstanding but not included in the computation of diluted earnings per share of common stock because performance conditions had not yet been met.