Accounting Policies - Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Earnings Per Share, Basic [Abstract]
Net income attributable to common stockholders	$ 16,190		$ 22,203
Weighted-average shares, basic (shares)	10,737		10,365
Basic earnings per common share (dollars per share)	$ 1.51		$ 2.14
Dilutive Securities, Effect on Basic Earnings Per Share [Abstract]
Weighted-average shares, dilutive securities, stock options, SARs, and restricted stock (shares)	424	[1]	538	[1]
Earnings Per Share, dilutive securities, stock options, SARs, and restricted stock (dollars per share)	$ (0.06)	[1]	$ (0.10)	[1]
Net (loss)/Income income attributable to common stockholders, diluted	$ 16,190		$ 22,203
Weighted-average shares, diluted (shares)	11,161		10,903
Diluted Earnings per common share	$ 1.45		$ 2.04

[1] For the three months ended March 31, 2013 and 2012, stock options and SARs of 4,000 and 582,447, 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, 2013 and 2012, contingent shares of non-vested restricted stock of 25,300 and 79,300, respectively, were outstanding but not included in the computation of diluted earnings per share of common stock because performance conditions were not me