Fair Value Measurements (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014
Fair Value Measurements
Assets, Fair Value	$ 0
Liabilities, Fair Value	0
Foreign Exchange Contract \| Other Income Expense \| Not Designated as Hedging Instrument
Fair Value Measurements
Foreign exchange contracts	$ 200
Minimum
Fair Value Measurements
Maturity period of long-term investments	1 year
Maximum
Fair Value Measurements
Maturity period of long-term investments	2 years
Measured on a recurring basis
Fair Value Measurements
Adjusted cost, Available-for-sale investments	$ 81,068
Unrealized Gains, available-for-sale investments	2
Unrealized Losses, available-for-sale investments	(63)
Fair value, Available-for-sale investments	81,007
Assets, Adjusted Cost		$ 97,266
Assets, Unrealized Gains		2
Assets, Unrealized Losses		(49)
Assets, Fair Value		97,219
Measured on a recurring basis \| Cash and Cash Equivalents
Fair Value Measurements
Assets, Fair Value	29,530	29,187
Measured on a recurring basis \| Short-term investments
Fair Value Measurements
Assets, Fair Value	37,761	53,523
Measured on a recurring basis \| Long-term investments
Fair Value Measurements
Assets, Fair Value	13,716	14,509
Measured on a recurring basis \| Cash
Fair Value Measurements
Adjusted cost, Available-for-sale investments	7,593
Fair value, Available-for-sale investments	7,593
Assets, Adjusted Cost		13,077
Assets, Fair Value		13,077
Measured on a recurring basis \| Cash \| Cash and Cash Equivalents
Fair Value Measurements
Assets, Fair Value	7,593	13,077
Measured on a recurring basis \| Level 1
Fair Value Measurements
Adjusted cost, Available-for-sale investments	22,935
Unrealized Losses, available-for-sale investments	(2)
Fair value, Available-for-sale investments	22,933
Assets, Adjusted Cost		16,110
Assets, Fair Value		16,110
Measured on a recurring basis \| Level 1 \| Cash and Cash Equivalents
Fair Value Measurements
Assets, Fair Value	21,937	16,110
Measured on a recurring basis \| Level 1 \| Long-term investments
Fair Value Measurements
Assets, Fair Value	996
Measured on a recurring basis \| Level 1 \| Money market funds
Fair Value Measurements
Adjusted cost, Available-for-sale investments	21,937
Fair value, Available-for-sale investments	21,937
Assets, Adjusted Cost		16,110
Assets, Fair Value		16,110
Measured on a recurring basis \| Level 1 \| Money market funds \| Cash and Cash Equivalents
Fair Value Measurements
Assets, Fair Value	21,937	16,110
Measured on a recurring basis \| Level 1 \| U.S. government notes
Fair Value Measurements
Adjusted cost, Available-for-sale investments	998
Unrealized Losses, available-for-sale investments	(2)
Fair value, Available-for-sale investments	996
Measured on a recurring basis \| Level 1 \| U.S. government notes \| Long-term investments
Fair Value Measurements
Assets, Fair Value	996
Measured on a recurring basis \| Level 2
Fair Value Measurements
Adjusted cost, Available-for-sale investments	50,540	68,079
Unrealized Gains, available-for-sale investments	2	2
Unrealized Losses, available-for-sale investments	(61)	(49)
Fair value, Available-for-sale investments	50,481	68,032
Measured on a recurring basis \| Level 2 \| Short-term investments
Fair Value Measurements
Fair value, Available-for-sale investments	37,761	53,523
Measured on a recurring basis \| Level 2 \| Long-term investments
Fair Value Measurements
Fair value, Available-for-sale investments	12,720	14,509
Measured on a recurring basis \| Level 2 \| Asset-backed securities
Fair Value Measurements
Adjusted cost, Available-for-sale investments	6,739	4,458
Unrealized Losses, available-for-sale investments	(9)	(3)
Fair value, Available-for-sale investments	6,730	4,455
Measured on a recurring basis \| Level 2 \| Asset-backed securities \| Long-term investments
Fair Value Measurements
Fair value, Available-for-sale investments	6,730	4,455
Measured on a recurring basis \| Level 2 \| Corporate bonds
Fair Value Measurements
Adjusted cost, Available-for-sale investments	39,195	54,321
Unrealized Gains, available-for-sale investments	2	2
Unrealized Losses, available-for-sale investments	(51)	(46)
Fair value, Available-for-sale investments	39,146	54,277
Measured on a recurring basis \| Level 2 \| Corporate bonds \| Short-term investments
Fair Value Measurements
Fair value, Available-for-sale investments	33,156	46,726
Measured on a recurring basis \| Level 2 \| Corporate bonds \| Long-term investments
Fair Value Measurements
Fair value, Available-for-sale investments	5,990	7,551
Measured on a recurring basis \| Level 2 \| Commercial paper
Fair Value Measurements
Adjusted cost, Available-for-sale investments	1,100	6,797
Fair value, Available-for-sale investments	1,100	6,797
Measured on a recurring basis \| Level 2 \| Commercial paper \| Short-term investments
Fair Value Measurements
Fair value, Available-for-sale investments	1,100	6,797
Measured on a recurring basis \| Level 2 \| U.S. agency securities
Fair Value Measurements
Adjusted cost, Available-for-sale investments	3,506	2,503
Unrealized Losses, available-for-sale investments	(1)
Fair value, Available-for-sale investments	3,505	2,503
Measured on a recurring basis \| Level 2 \| U.S. agency securities \| Short-term investments
Fair Value Measurements
Fair value, Available-for-sale investments	$ 3,505
Measured on a recurring basis \| Level 2 \| U.S. agency securities \| Long-term investments
Fair Value Measurements
Fair value, Available-for-sale investments		$ 2,503

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Represents the unrealized gains of cash and cash equivalents and investments.

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Represents the unrealized losses of cash and cash equivalents and investments.

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Represents the maturity period of long-term investments.

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Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Fair value of financial obligations, including, but not limited to, debt instruments, derivative liabilities, federal funds purchased and sold under agreements to repurchase, securities loaned or sold under agreements to repurchase, financial instruments sold not yet purchased, guarantees, line of credit, loans and notes payable, servicing liability, and trading liabilities.

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