Financial Instruments (Fair Value Measurements) (Details) - Measured on a recurring basis - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Fair Value Measurements
Adjusted Cost, assets	$ 47,724	$ 81,068
Unrealized Gains, available-for-sale securities	16	2
Unrealized Losses, available-for-sale securities	(3)	(63)
Fair Value, assets	47,737	81,007
Cash and Cash Equivalents
Fair Value Measurements
Fair Value, available-for-sale investments	17,004	29,530
Short-term investments
Fair Value Measurements
Fair Value, available-for-sale investments	24,002	37,761
Long-term investments
Fair Value Measurements
Fair Value, available-for-sale investments	6,732	13,716
Cash
Fair Value Measurements
Fair value, cash and cash equivalents	6,342	7,593
Cash \| Cash and Cash Equivalents
Fair Value Measurements
Fair value, cash and cash equivalents	6,342	7,593
Level 1
Fair Value Measurements
Adjusted Cost, assets	11,660	22,935
Unrealized Gains, available-for-sale securities	1
Unrealized Losses, available-for-sale securities		(2)
Fair Value, assets	11,661	22,933
Level 1 \| Cash and Cash Equivalents
Fair Value Measurements
Fair Value, available-for-sale investments	10,662	21,937
Level 1 \| Short-term investments
Fair Value Measurements
Fair Value, available-for-sale investments	999
Level 1 \| Long-term investments
Fair Value Measurements
Fair Value, available-for-sale investments		996
Level 1 \| Money market funds
Fair Value Measurements
Fair value, cash and cash equivalents	10,662	21,937
Level 1 \| Money market funds \| Cash and Cash Equivalents
Fair Value Measurements
Fair value, cash and cash equivalents	10,662	21,937
Level 1 \| U.S. government notes
Fair Value Measurements
Adjusted Cost, available-for-sale securities	998	998
Unrealized Gains, available-for-sale securities	1
Unrealized Losses, available-for-sale securities		(2)
Fair Value, available-for-sale investments	999	996
Level 1 \| U.S. government notes \| Short-term investments
Fair Value Measurements
Fair Value, available-for-sale investments	999
Level 1 \| U.S. government notes \| Long-term investments
Fair Value Measurements
Fair Value, available-for-sale investments		996
Level 2
Fair Value Measurements
Adjusted Cost, available-for-sale securities		50,540
Unrealized Gains, available-for-sale securities		2
Unrealized Losses, available-for-sale securities		(61)
Fair Value, available-for-sale investments		50,481
Level 2 \| Short-term investments
Fair Value Measurements
Fair Value, available-for-sale investments		37,761
Level 2 \| Long-term investments
Fair Value Measurements
Fair Value, available-for-sale investments		12,720
Level 2 \| Available-for-sale investments
Fair Value Measurements
Adjusted Cost, available-for-sale securities	29,722
Unrealized Gains, available-for-sale securities	15
Unrealized Losses, available-for-sale securities	(3)
Fair Value, available-for-sale investments	29,734
Level 2 \| Available-for-sale investments \| Short-term investments
Fair Value Measurements
Fair Value, available-for-sale investments	23,003
Level 2 \| Available-for-sale investments \| Long-term investments
Fair Value Measurements
Fair Value, available-for-sale investments	6,732
Level 2 \| Asset-backed securities
Fair Value Measurements
Adjusted Cost, available-for-sale securities	5,334	6,739
Unrealized Gains, available-for-sale securities	3
Unrealized Losses, available-for-sale securities		(9)
Fair Value, available-for-sale investments	5,337	6,730
Level 2 \| Asset-backed securities \| Short-term investments
Fair Value Measurements
Fair Value, available-for-sale investments	28
Level 2 \| Asset-backed securities \| Long-term investments
Fair Value Measurements
Fair Value, available-for-sale investments	5,308	6,730
Level 2 \| Corporate bonds
Fair Value Measurements
Adjusted Cost, available-for-sale securities	22,887	39,195
Unrealized Gains, available-for-sale securities	11	2
Unrealized Losses, available-for-sale securities	(3)	(51)
Fair Value, available-for-sale investments	22,895	39,146
Level 2 \| Corporate bonds \| Short-term investments
Fair Value Measurements
Fair Value, available-for-sale investments	21,473	33,156
Level 2 \| Corporate bonds \| Long-term investments
Fair Value Measurements
Fair Value, available-for-sale investments	1,424	5,990
Level 2 \| Commercial paper
Fair Value Measurements
Adjusted Cost, available-for-sale securities		1,100
Fair Value, available-for-sale investments		1,100
Level 2 \| Commercial paper \| Short-term investments
Fair Value Measurements
Fair Value, available-for-sale investments		1,100
Level 2 \| U.S. agency securities
Fair Value Measurements
Adjusted Cost, available-for-sale securities	1,501	3,506
Unrealized Gains, available-for-sale securities	1
Unrealized Losses, available-for-sale securities		(1)
Fair Value, available-for-sale investments	1,502	3,505
Level 2 \| U.S. agency securities \| Short-term investments
Fair Value Measurements
Fair Value, available-for-sale investments	$ 1,502	$ 3,505

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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.

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

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Fair value portion 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.

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