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Subsequent Events - Additional Information (Detail) (USD $)
In Millions, except Share data, unless otherwise specified |
1 Months Ended | 1 Months Ended | |||
|---|---|---|---|---|---|
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Mar. 31, 2011
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Dec. 31, 2012
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Dec. 31, 2011
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Feb. 01, 2013
Subsequent Event [Member]
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Feb. 04, 2013
Subsequent Event [Member]
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| Subsequent Event [Line Items] | |||||
| Debt instrument offering date | Feb. 01, 2013 | ||||
| Aggregate principal amount | $ 3,470.0 | $ 3,033.0 | $ 500.0 | ||
| Secondary offering of common stock | 30,000,000 | 30,000,000 | |||
| Public offering of common stock, price per share | $ 30.00 | $ 30.35 | |||
| Percentage of common shares held by stockholders | 42.00% | ||||
| Secondary offering of common shares, closing date | February 7, 2013 | ||||
| Debt instrument, interest rate | 5.75% | ||||
| Debt instrument, due date | 2021 | ||||