Quarterly report pursuant to Section 13 or 15(d)

Significant Accounting Policies - Effects of Prior Period Errors in Consolidated Statements of Income (Detail)

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Significant Accounting Policies - Effects of Prior Period Errors in Consolidated Statements of Income (Detail) (USD $)
In Thousands, except Per Share data, unless otherwise specified
 3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Income taxes $ 43,636 $ 51,586 $ 88,311 $ 96,387 $ 186,944 $ 144,820 $ 87,212
Net income 143,162 131,951 262,035 239,882 463,962 414,959 292,883
Basic earnings per share $ 1.39 $ 1.13 $ 2.53 $ 2.06 $ 4.13 $ 3.53 $ 2.46
Diluted earnings per share $ 1.34 $ 1.09 $ 2.44 $ 1.96 $ 3.94 $ 3.32 $ 2.32
As Previously Reported [Member]
              
Income taxes   50,169   94,739 173,716 147,201 80,880
Net income   $ 133,368   $ 241,530 $ 477,190 $ 412,578 $ 299,215
Basic earnings per share   $ 1.14   $ 2.08 $ 4.25 $ 3.51 $ 2.51
Diluted earnings per share   $ 1.10   $ 1.98 $ 4.05 $ 3.30 $ 2.37