Summary of Significant Accounting Policies - Reconciliation of the Basic and Diluted EPS Denominators (Details) - shares shares in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of the basic and diluted EPS denominators
Basic weighted-average common shares	32,488	32,415	30,968
Dilutive effect of restricted common stock	218	444	603
Dilutive effect of 2010 Convertible Notes			1,062
Dilutive effect of Stock Warrants	149	6	381
Diluted weighted-average common shares	32,855	32,865	33,014

Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of call options and warrants using the treasury stock method.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of convertible debt securities using the if-converted method.

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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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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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