Accounting Policies - Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2015		Jun. 30, 2014		Jun. 30, 2015		Jun. 30, 2014
Accounting Policies [Abstract]
Net income attributable to common stockholders (Dilutive)	$ 22,162		$ 20,205		$ 23,980		$ 21,018
Stock options, SARs and restricted stock	428	[1]	437	[1]	411	[2]	448	[2]
Stock options, SARs and restricted stock (in usd per share)	$ (0.07)	[1]	$ (0.07)	[1]	$ (0.08)	[2]	$ (0.08)	[2]
Weighted Average Number of Shares Outstanding, Diluted	11,438		11,361		11,385		11,354
Diluted earnings per common share	$ 1.94		$ 1.78		$ 2.11		$ 1.85
Earnings Per Share, Basic [Abstract]
Net income attributable to common stockholders (Basic)	$ 22,162		$ 20,205		$ 23,980		$ 21,018
Weighted Average Number of Shares Outstanding, Basic	11,010		10,924		10,974		10,906
Basic earnings per common share	$ 2.01		$ 1.85		$ 2.19		$ 1.93

[1] For the three months ended June 30, 2015 and 2014, stock options and SARs of 229,693 and 121,468, 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 June 30, 2015 and 2014, contingent shares of non-vested restricted stock of 45,034 and 42,514, respectively, were outstanding but not included in the computation of diluted earnings per share of common stock because performance conditions have not yet been met.

[2] For the six months ended June 30, 2015 and 2014, stock options and SARs of 215,547 and 77,226, respectively, were outstanding but not included in the computation of diluted earnings per share of common stock because they were anti-dilutive. For the six months ended June 30, 2015 and 2014, contingent shares of non-vested restricted stock of 37,774 and 37,054, respectively, were outstanding but not included in the computation of diluted earnings per share of common stock because performance conditions have not yet been met.