Organization and Summary of Significant Accounting Policies - Additional Information (Detail)	3 Months Ended	6 Months Ended
Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Jun. 30, 2014	Jun. 30, 2015 USD ($) Segment	Jun. 30, 2014	Dec. 31, 2014 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash and investments in marketable securities	$ 279,660,000			$ 279,660,000		$ 262,824,000
Senior secured notes	125,000,000			125,000,000		125,000,000
Long-term debt	133,500,000			133,500,000
Capital lease obligations	8,500,000			8,500,000
Capital lease obligations, current portion	$ 5,643,000			$ 5,643,000		$ 4,512,000
Number of business segments \| Segment				1
Asset impairment charges		$ 0		$ 0
Effective income tax rate	34.00%		34.00%	34.00%	34.00%

Cash, Restricted Cash, Cash Equivalents, And Available For Sale Investments

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Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date.

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Amount of capital lease obligation due within one year or the normal operating cycle, if longer.

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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Carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer), excluding current portion. Senior note holders are paid off in full before any payments are made to junior note holders.

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