Quarterly report pursuant to Section 13 or 15(d)

Earnings Per Share (Schedule of Calculation of Basic and Diluted Earnings Per Common Share) (Detail)

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Earnings Per Share (Schedule of Calculation of Basic and Diluted Earnings Per Common Share) (Detail) (USD $)
In Thousands, except Per Share data, unless otherwise specified
3 Months Ended 9 Months Ended
Sep. 30, 2012
Sep. 30, 2011
Sep. 30, 2012
Sep. 30, 2011
Earnings Per Share [Line Items]        
Net income (loss) $ (1,471) $ 52,928 $ 55,315 $ 126,752
Less portion distributed and allocated to nonvested shares 90 1,118 1,128 2,680
Net income (loss) allocated to common shares $ (1,561) $ 51,810 $ 54,187 $ 124,072
Weighted average common shares outstanding 74,327 74,028 74,315 74,017
Basic and diluted earnings (loss) per common share $ (0.02) $ 0.70 $ 0.73 $ 1.68
Shares excluded due to being anti-dilutive (weighted-average) 1,866 1,995 1,823 1,798