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Nature of Business and Basis of Presentation - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Cash and cash equivalents	161,195us-gaap_CashAndCashEquivalentsAtCarryingValue	$ 119,539us-gaap_CashAndCashEquivalentsAtCarryingValue	$ 164,278us-gaap_CashAndCashEquivalentsAtCarryingValue	$ 191,514us-gaap_CashAndCashEquivalentsAtCarryingValue
Convertible Debt | 2012 Notes
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Convertible senior notes, earliest redemption date	Jan. 19, 2017
Convertible Debt | 2014 Notes
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Convertible senior notes, earliest redemption date	Jan. 19, 2019

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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-Name Accounting Standards Codification

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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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-Publisher FASB

-Name Accounting Standards Codification

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-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21475-112644



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