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Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands | 3 Months Ended | 12 Months Ended
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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

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