Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Undistributed Earnings (Loss) Allocated to Participating Securities, Diluted									$ 3,595	$ 3,468	$ 4,599
Basic and Diluted Earnings per share
Weighted average basic common shares outstanding									23,148	23,380	23,096
Dilutive effect of contingently convertible notes and warrants									0	1,499	2,213
Dilutive effect of employee stock purchases, net of assumed repurchase of treasury stock									4	6	5
Weighted average dilutive common shares outstanding									23,152	24,885	25,314
Basic:
Net income									$ 93,999	$ 93,004	$ 113,992
Undistributed Earnings (Loss) Allocated to Participating Securities, Basic									3,595	3,643	4,963
Earnings available to basic common shares									$ 90,404	$ 89,361	$ 109,029
Basic earnings per common share	$ (1.41)	$ 1.88	$ 1.91	$ 1.47	$ 0.77	$ 1.07	$ 0.70	$ 1.29	$ 3.91	$ 3.82	$ 4.72
Diluted:
Net income									$ 93,999	$ 93,004	$ 113,992
Earnings available to diluted common shares									$ 90,404	$ 89,536	$ 109,393
Diluted earnings per common share	$ (1.41)	$ 1.88	$ 1.91	$ 1.47	$ 0.77	$ 1.03	$ 0.62	$ 1.19	$ 3.90	$ 3.60	$ 4.32