Annual report pursuant to Section 13 and 15(d)

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

v2.4.0.6
Schedule of Calculation of Basic Earnings Per Common Share (Detail) (USD $)
In Thousands, except Per Share data, unless otherwise specified
 3 Months Ended 12 Months Ended
Dec. 31, 2012
Sep. 30, 2012
Jun. 30, 2012
Mar. 31, 2012
Dec. 31, 2011
Sep. 30, 2011
Jun. 30, 2011
Mar. 31, 2011
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Earnings Per Share [Line Items]                      
Net income $ 16,670 $ (1,471) $ 53,567 $ 3,218 $ 46,065 $ 52,928 $ 55,175 $ 18,649 $ 71,984 $ 172,817 $ 117,892
Less portion allocated to nonvested shares                 983 3,211 1,178
Net income allocated to common shares                 $ 71,001 $ 169,606 $ 116,714
Weighted average common shares outstanding                 74,354 74,033 73,685
Basic and diluted earnings per common share $ 0.21 [1] $ (0.02) [1] $ 0.70 [1] $ 0.04 [1] $ 0.61 [1] $ 0.70 [1] $ 0.73 [1] $ 0.25 [1] $ 0.95 $ 2.29 $ 1.58
Shares excluded due to being anti-dilutive                 1,923 1,873 1,540
[1] The sum of the individual quarterly earnings per share may not agree with year-to-date earnings per share because each quarterly calculation is based on the income for that quarter and the weighted average number of shares outstanding during that quarter.