Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Undistributed Earnings (Loss) Allocated to Participating Securities, Diluted									$ 5,869	$ 3,595	$ 3,468
Basic and Diluted Earnings per share
Weighted average basic common shares outstanding									21,161	23,148	23,380
Dilutive effect of contingently convertible notes and warrants									0	0	1,499
Dilutive effect of employee stock purchases, net of assumed repurchase of treasury stock									9	4	6
Weighted average dilutive common shares outstanding									21,170	23,152	24,885
Basic:
Net income									$ 147,065	$ 93,999	$ 93,004
Undistributed Earnings (Loss) Allocated to Participating Securities, Basic									5,871	3,595	3,643
Earnings available to basic common shares									$ 141,194	$ 90,404	$ 89,361
Basic earnings per common share	$ 1.44	$ 1.65	$ 2.12	$ 1.47	$ (1.41)	$ 1.88	$ 1.91	$ 1.47	$ 6.67	$ 3.91	$ 3.82
Diluted:
Net income									$ 147,065	$ 93,999	$ 93,004
Earnings available to diluted common shares									$ 141,196	$ 90,404	$ 89,536
Diluted earnings per common share	$ 1.44	$ 1.65	$ 2.12	$ 1.47	$ (1.41)	$ 1.88	$ 1.91	$ 1.47	$ 6.67	$ 3.90	$ 3.60