Earnings per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Numerator
Net income	$ 69,002us-gaap_NetIncomeLoss	$ 37,706us-gaap_NetIncomeLoss
Denominator
Weighted-average shares outstanding, basic	73,054	72,684
Effect of dilutive stock awards (in shares)	316	570
Adjusted weighted-average shares outstanding, diluted	73,370	73,254
Net income per share
Basic earnings per common share (in dollars per share)	$ 0.94us-gaap_EarningsPerShareBasic	$ 0.52us-gaap_EarningsPerShareBasic
Diluted earnings per common share (in dollars per share)	$ 0.94us-gaap_EarningsPerShareDiluted	$ 0.51us-gaap_EarningsPerShareDiluted
Anti-dilutive weighted-average shares	27	56

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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