Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Earnings Per Share [Abstract]
Net income	$ 28,486us-gaap_NetIncomeLoss	$ 37,884us-gaap_NetIncomeLoss
Average common shares outstanding - basic	27,301,000	27,094,000
Additional shares for stock based compensation plans	68,000	32,000
Average common shares outstanding - diluted	27,369,000	27,126,000
Earnings per share of common stock - basic	$ 1.04us-gaap_EarningsPerShareBasic	$ 1.40us-gaap_EarningsPerShareBasic
Earnings per share of common stock - diluted	$ 1.04us-gaap_EarningsPerShareDiluted	$ 1.40us-gaap_EarningsPerShareDiluted
Earnings Per Share, Diluted, Other Disclosures [Abstract]
Antidilutive Shares Excluded from Net Income Per Diluted Common Share Calculation	28,000	44,000

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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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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The sum of dilutive potential common shares or units used in the calculation of the diluted per-share or per-unit computation.

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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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