Reconciliation of Earnings Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share [Abstract]
Net income for basic and diluted earnings per share	$ 4,491	$ 18,600	$ 35,202	$ 52,574
Weighted average shares outstanding - basic	36,676	36,873	36,670	36,866
Dilutive effect of stock options and restricted stock	182	177	129	130
Weighted average shares outstanding - diluted	36,858	37,050	36,799	36,996
Earnings per share - basic	$ 0.12	$ 0.50	$ 0.96	$ 1.43
Earnings per share - diluted	$ 0.12	$ 0.50	$ 0.96	$ 1.42

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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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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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