Accounting Policies - Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounting Policies [Abstract]
Net income attributable to common stockholders (Basic)	$ 5,647	$ 11,586	$ 20,205	$ 813	$ 12,485	$ 15,413	$ 27,745	$ 16,190	$ 38,251	$ 71,833	$ 43,894
Net income attributable to common stockholders (Dilutive)									$ 38,251	$ 71,833	$ 43,894
Earnings Per Share, Basic [Abstract]
Stock options, SARs and restricted stock									447	393	540
Stock options, SARs and restricted stock (in usd per share)									$ (0.13)	$ (0.23)	$ (0.21)
Weighted Average Number of Shares Outstanding, Basic									10,920	10,816	10,479
Basic earnings per common share	$ 0.52	$ 1.06	$ 1.85	$ 0.07	$ 1.14	$ 1.42	$ 2.57	$ 1.51	$ 3.50	$ 6.64	$ 4.19
Weighted Average Number of Shares Outstanding, Diluted									11,367	11,209	11,019
Diluted earnings per common share	$ 0.50	$ 1.02	$ 1.78	$ 0.07	$ 1.11	$ 1.37	$ 2.48	$ 1.45	$ 3.37	$ 6.41	$ 3.98