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Nature of Business and Basis of Presentation - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	0 Months Ended					6 Months Ended
	Oct. 22, 2013	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2014 Convertible Debt 2012 Notes	Jun. 30, 2014 Convertible Debt 2014 Notes
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Reduction in staff positions	50.00%
Cash and cash equivalents		$ 150,528	$ 191,514	$ 149,426	$ 260,242
Convertible senior notes, earliest redemption date						Jan. 19, 2017	Jan. 19, 2019

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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