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Nature of Business and Basis of Presentation - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Cash and cash equivalents	$ 201,780	$ 260,242	$ 245,822	$ 116,602
Convertible senior notes, earliest redemption date	Jan. 19, 2017

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Earliest date before maturity when the issuer can call the outstanding debt instrument for repayment or conversion to equity, in CCYY-MM-DD format.

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