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Net Income Per Share (Details) - USD ($) shares in Thousands, $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2016 | Sep. 30, 2016 | Jun. 30, 2016 | Mar. 31, 2016 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Earnings Per Share [Abstract] |  |  |  |  |  |  |  |  |  |  |
Net income | $ 15,554 | $ 19,202 | $ 14,018 | $ 35,628 | $ 9,520 | $ 14,065 | $ 9,713 | $ 32,693 | $ 84,402 | $ 65,991 | $ 39,390
Less distributed and undistributed earnings allocated to participating securities |  |  |  |  |  |  |  |  | 1,517 | 1,496 | 981
Net income allocated to common shares |  |  |  |  |  |  |  |  | $ 82,885 | $ 64,495 | $ 38,409
Weighted average common shares outstanding |  |  |  |  |  |  |  |  | 41,067 | 41,668 | 48,616
Incremental shares from assumed conversions of common stock options and LTIP awards |  |  |  |  |  |  |  |  | 204 | 94 | 14
Adjusted weighted average common shares outstanding |  |  |  |  |  |  |  |  | 41,271 | 41,762 | 48,630
Potentially dilutive securities not included in weighted average share calculation due to anti-dilutive effect |  |  |  |  |  |  |  |  | 0 | 0 | 0

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