Fair Value Accounting - Recurring Basis (Details) - USD ($)	Jun. 30, 2015	Dec. 31, 2014
Marketable Securities, Current [Abstract]
Fair value, current	$ 21,647,000	$ 29,815,000
Marketable Securities, Noncurrent [Abstract]
Fair value, non-current	9,683,000	16,012,000
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	36,056,000	51,123,000
Commercial paper
Marketable Securities, Current [Abstract]
Fair value, current		1,998,000
Commercial paper \| Fair Value, Measurements, Recurring [Member]
Marketable Securities, Current [Abstract]
Fair value, current		1,998,000
Corporate notes and bonds
Marketable Securities, Current [Abstract]
Fair value, current	19,077,000	24,436,000
Marketable Securities, Noncurrent [Abstract]
Fair value, non-current	8,682,000	15,014,000
Corporate notes and bonds \| Fair Value, Measurements, Recurring [Member]
Marketable Securities, Current [Abstract]
Fair value, current	19,077,000	24,436,000
Marketable Securities, Noncurrent [Abstract]
Fair value, non-current	8,682,000	15,014,000
Agency securities
Marketable Securities, Noncurrent [Abstract]
Fair value, non-current	1,001,000	998,000
Agency securities \| Fair Value, Measurements, Recurring [Member]
Marketable Securities, Noncurrent [Abstract]
Fair value, non-current	1,001,000	998,000
Mortgage securities
Marketable Securities, Current [Abstract]
Fair value, current	2,570,000	3,381,000
Mortgage securities \| Fair Value, Measurements, Recurring [Member]
Marketable Securities, Current [Abstract]
Fair value, current	2,570,000	3,381,000
Cash \| Fair Value, Measurements, Recurring [Member]
Cash and cash equivalents:
Cash and Cash Equivalents, Fair Value Disclosure	2,149,000	2,701,000
Money market funds \| Fair Value, Measurements, Recurring [Member]
Cash and cash equivalents:
Cash and Cash Equivalents, Fair Value Disclosure	2,577,000	2,595,000
Fair Value, Inputs, Level 1 [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	4,726,000	5,296,000
Fair Value, Inputs, Level 1 [Member] \| Commercial paper \| Fair Value, Measurements, Recurring [Member]
Marketable Securities, Current [Abstract]
Fair value, current		0
Fair Value, Inputs, Level 1 [Member] \| Corporate notes and bonds \| Fair Value, Measurements, Recurring [Member]
Marketable Securities, Current [Abstract]
Fair value, current	0	0
Marketable Securities, Noncurrent [Abstract]
Fair value, non-current	0	0
Fair Value, Inputs, Level 1 [Member] \| Agency securities \| Fair Value, Measurements, Recurring [Member]
Marketable Securities, Noncurrent [Abstract]
Fair value, non-current	0	0
Fair Value, Inputs, Level 1 [Member] \| Mortgage securities \| Fair Value, Measurements, Recurring [Member]
Marketable Securities, Current [Abstract]
Fair value, current	0	0
Fair Value, Inputs, Level 1 [Member] \| Cash \| Fair Value, Measurements, Recurring [Member]
Cash and cash equivalents:
Cash and Cash Equivalents, Fair Value Disclosure	2,149,000	2,701,000
Fair Value, Inputs, Level 1 [Member] \| Money market funds \| Fair Value, Measurements, Recurring [Member]
Cash and cash equivalents:
Cash and Cash Equivalents, Fair Value Disclosure	2,577,000	2,595,000
Fair Value, Inputs, Level 2 [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	28,760,000	42,446,000
Fair Value, Inputs, Level 2 [Member] \| Commercial paper \| Fair Value, Measurements, Recurring [Member]
Marketable Securities, Current [Abstract]
Fair value, current		1,998,000
Fair Value, Inputs, Level 2 [Member] \| Corporate notes and bonds \| Fair Value, Measurements, Recurring [Member]
Marketable Securities, Current [Abstract]
Fair value, current	19,077,000	24,436,000
Marketable Securities, Noncurrent [Abstract]
Fair value, non-current	8,682,000	15,014,000
Fair Value, Inputs, Level 2 [Member] \| Agency securities \| Fair Value, Measurements, Recurring [Member]
Marketable Securities, Noncurrent [Abstract]
Fair value, non-current	1,001,000	998,000
Fair Value, Inputs, Level 2 [Member] \| Mortgage securities \| Fair Value, Measurements, Recurring [Member]
Marketable Securities, Current [Abstract]
Fair value, current	0	0
Fair Value, Inputs, Level 2 [Member] \| Cash \| Fair Value, Measurements, Recurring [Member]
Cash and cash equivalents:
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Fair Value, Inputs, Level 2 [Member] \| Money market funds \| Fair Value, Measurements, Recurring [Member]
Cash and cash equivalents:
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Fair Value, Inputs, Level 3 [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	2,570,000	3,381,000
Fair Value, Inputs, Level 3 [Member] \| Commercial paper \| Fair Value, Measurements, Recurring [Member]
Marketable Securities, Current [Abstract]
Fair value, current		0
Fair Value, Inputs, Level 3 [Member] \| Corporate notes and bonds \| Fair Value, Measurements, Recurring [Member]
Marketable Securities, Current [Abstract]
Fair value, current	0	0
Marketable Securities, Noncurrent [Abstract]
Fair value, non-current	0	0
Fair Value, Inputs, Level 3 [Member] \| Agency securities \| Fair Value, Measurements, Recurring [Member]
Marketable Securities, Noncurrent [Abstract]
Fair value, non-current	0	0
Fair Value, Inputs, Level 3 [Member] \| Mortgage securities \| Fair Value, Measurements, Recurring [Member]
Marketable Securities, Current [Abstract]
Fair value, current	2,570,000	3,381,000
Fair Value, Inputs, Level 3 [Member] \| Cash \| Fair Value, Measurements, Recurring [Member]
Cash and cash equivalents:
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Fair Value, Inputs, Level 3 [Member] \| Money market funds \| Fair Value, Measurements, Recurring [Member]
Cash and cash equivalents:
Cash and Cash Equivalents, Fair Value Disclosure	$ 0	$ 0

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)

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Amount of investment in debt and equity securities categorized neither as trading securities nor held-to-maturity securities and intended be sold or mature one year or operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

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Investments in debt and equity securities which are categorized neither as held-to-maturity nor trading and which are intended to be sold or mature more than one year from the balance sheet date or operating cycle, if longer. Such securities are reported at fair value; unrealized gains (losses) related to Available-for-sale Securities are excluded from earnings and reported in a separate component of shareholders' equity (other comprehensive income), unless the Available-for-sale security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain (loss) of an Available-for-sale security that is designated as being hedged in a fair value hedge is recognized in earnings during the period of the hedge, as are other than temporary declines in fair value below the cost basis for investments in equity securities and debt securities that an entity intends to sell or it is more likely than not that it will be required to sell before the recovery of its amortized cost basis. Other than temporary declines in fair value below the cost basis for debt securities categorized as Available-for-sale that an entity does not intend to sell and for which it is not more likely than not that the entity will be required to sell before the recovery of its amortized cost basis are bifurcated into credit losses and losses related to all other factors. Other than temporary declines in fair value below cost basis related to credit losses are recognized in earnings, and losses related to all other factors are recognized in other comprehensive income.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Available-for-Sale Securities

-URI http://asc.fasb.org/extlink&oid=6505594

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

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-Section 45

-Paragraph 2

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash

-URI http://asc.fasb.org/extlink&oid=6506951

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

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