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Summary of Investments Classified as Available-For-Sale Securities (Detail) (USD $)
In Thousands, unless otherwise specified

3 Months Ended

12 Months Ended

Mar. 31, 2013

Dec. 31, 2012

Schedule of Available-for-sale Securities [Line Items]

144,133

109,741

Gross Unrealized Gains

22

^[1]

33

^[1]

Gross Unrealized Losses

(66)

^[1]

(35)

^[1]

Aggregate Estimated Fair Value

144,089

109,739

Short-term investments

Schedule of Available-for-sale Securities [Line Items]

126,706

109,261

Gross Unrealized Gains

22

^[1]

33

^[1]

Gross Unrealized Losses

(49)

^[1]

(35)

^[1]

Aggregate Estimated Fair Value

126,679

109,259

Short-term investments | Certificates of deposit

Schedule of Available-for-sale Securities [Line Items]

9,560

11,960

Gross Unrealized Losses

(10)

^[1]

(6)

^[1]

Aggregate Estimated Fair Value

9,550

11,954

Short-term investments | Certificates of deposit | Maximum

Schedule of Available-for-sale Securities [Line Items]

Available for sale securities contractual maturity

1 year

1 year

Short-term investments | Commercial paper

Schedule of Available-for-sale Securities [Line Items]

26,571

19,713

Gross Unrealized Losses

(7)

^[1]

(18)

^[1]

Aggregate Estimated Fair Value

26,564

Short-term investments | Commercial paper | Maximum

Schedule of Available-for-sale Securities [Line Items]

Available for sale securities contractual maturity

1 year

1 year

Short-term investments | Corporate debt securities

Schedule of Available-for-sale Securities [Line Items]

90,575

77,588

Gross Unrealized Gains

22

^[1]

33

^[1]

Gross Unrealized Losses

(32)

^[1]

(11)

^[1]

Aggregate Estimated Fair Value

90,565

77,610

Short-term investments | Corporate debt securities | Maximum

Schedule of Available-for-sale Securities [Line Items]

Available for sale securities contractual maturity

1 year

1 year

Long-term investments

Schedule of Available-for-sale Securities [Line Items]

17,427

480

Gross Unrealized Losses

(17)

^[1]

Aggregate Estimated Fair Value

17,410

480

Long-term investments | Certificates of deposit

Schedule of Available-for-sale Securities [Line Items]

1,440

480

Gross Unrealized Losses

(2)

^[1]

Aggregate Estimated Fair Value

1,438

480

Long-term investments | Certificates of deposit | Minimum

Schedule of Available-for-sale Securities [Line Items]

Available for sale securities contractual maturity

1 year

1 year

Long-term investments | Certificates of deposit | Maximum

Schedule of Available-for-sale Securities [Line Items]

Available for sale securities contractual maturity

2 years

2 years

Long-term investments | Corporate debt securities

Schedule of Available-for-sale Securities [Line Items]

8,487

Gross Unrealized Losses

(13)

^[1]

Aggregate Estimated Fair Value

8,474

Long-term investments | Corporate debt securities | Minimum

Schedule of Available-for-sale Securities [Line Items]

Available for sale securities contractual maturity

1 year

Long-term investments | Corporate debt securities | Maximum

Schedule of Available-for-sale Securities [Line Items]

Available for sale securities contractual maturity

2 years

Long-term investments | Securities of government sponsored entities

Schedule of Available-for-sale Securities [Line Items]

7,500

Gross Unrealized Losses

(2)

^[1]

Aggregate Estimated Fair Value

7,498

Long-term investments | Securities of government sponsored entities | Minimum

Schedule of Available-for-sale Securities [Line Items]

Available for sale securities contractual maturity

1 year

Long-term investments | Securities of government sponsored entities | Maximum

Schedule of Available-for-sale Securities [Line Items]

Available for sale securities contractual maturity

2 years

[1]	Unrealized gains and losses are included in other comprehensive loss.

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

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