Earnings Per Share Basic and Diluted, Per Share Amounts [Abstract]

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Income (Loss) Per Basic and Diluted Share [Abstract]

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Amount of increase (decrease) to net income used for calculating diluted earnings per share (EPS), resulting from the assumed exercise of stock options or restrictive stock units (RSUs).

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Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

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Net Income or Loss Available to Common Stockholders plus adjustments resulting from the assumption that dilutive convertible securities were converted, options or warrants were exercised, or that other shares were issued upon the satisfaction of certain conditions.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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Earnings Per Share (Details) - USD ($) $ / shares in Units, 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
Income (Numerator)
Income available to common stockholders, Basic									$ 144,877	$ 73,044	$ 74,479
Income available to common stockholders after assumed conversions, Diluted									$ 144,877	$ 73,044	$ 74,479
Weighted Shares (Denominator)
Weighted shares, basic (in shares)									55,316	55,249	55,157
Weighted shares, diluted (in shares)									55,327	55,302	55,209
Earnings Per Share Basic and Diluted, Per Share Amounts [Abstract]
Basic (in dollars per share)	$ 0.36	$ 0.84	$ 0.93	$ 0.49	$ (0.47)	$ 0.49	$ 0.88	$ 0.42	$ 2.62	$ 1.32	$ 1.35
Diluted (in dollars per share)	$ 0.36	$ 0.84	$ 0.93	$ 0.49	$ (0.47)	$ 0.49	$ 0.88	$ 0.42	$ 2.62	$ 1.32	$ 1.35
Common Stock [Member]
Earnings Per Share Basic and Diluted, Per Share Amounts [Abstract]
Potentially dilutive securities (in shares)									0	28	67
Stock Options [Member]
Income (Numerator)
Effect of dilutive securities: Options									$ 0	$ 0	$ 0
Weighted Shares (Denominator)
Effect of dilutive securities: options (in shares)									11	11	15
Restricted Stock Units (RSUs) [Member]
Income (Numerator)
Effect of dilutive securities: Options									$ 0	$ 0	$ 0
Weighted Shares (Denominator)
Effect of dilutive securities: options (in shares)									0	42	37