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Summary of Significant Accounting Policies - Additional Information (Detail)
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1 Months Ended |
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Nov. 30, 2012
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| Significant Accounting Policies [Line Items] | |
| Stock dividend payable date | Dec. 24, 2012 |
| stock dividend date of record | Dec. 10, 2012 |
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Common Class A
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| Significant Accounting Policies [Line Items] | |
| Stock split ratio for 100 percent of stock dividend declared | 2 |
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Common Class B
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| Significant Accounting Policies [Line Items] | |
| Stock split ratio for 100 percent of stock dividend declared | 2 |