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Convertible Senior Notes - Summary of Convertible Senior Notes (Parenthetical) (Detail) (Convertible Senior Notes 0.125% due April 1, 2019 [Member])
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3 Months Ended | |
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Mar. 31, 2015
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Mar. 31, 2014
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Convertible Senior Notes 0.125% due April 1, 2019 [Member]
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| Debt Instrument [Line Items] | ||
| Senior notes, Interest rate | 0.125% | 0.125% |
| Senior notes, Maturity date | Apr. 01, 2019 |