Fair value measurements - Additional Information (Detail) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Cash equivalents maturities	Three months or less
Realized gain (loss) on available-for-sale securities	$ 0	$ 0
Reclassification out of accumulated other comprehensive income	0	0
Unrealized Loss on Securities	134,400,000
Investments with other-than-temporary impairment	0
Contingent consideration, current	475,000
Contingent consideration, non current	$ 6,321,000
Minimum [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Milestone achievement period	2015
Milestone discount rates	10.80%
Maximum [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Milestone achievement period	2026
Milestone discount rates	14.80%
Certificates of Deposit [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Securities in unrealized loss position for less than twelve months, number of positions	52
U.S. Government Agency Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Securities in unrealized loss position for less than twelve months, number of positions	7

Fair value inputs expected milestone achievement period.

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Milestone discount rates.

+ References

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- Definition

An element designated to encapsulate any additional information related to cash and cash equivalents not otherwise addressed by the existing taxonomy. Cash includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Entity may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

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- Definition

This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 7

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-Topic 320

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-Section 50

-Paragraph 6

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- Definition

This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

+ References

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- Definition

Number of investment positions in available-for-sale investments in a continuous unrealized loss position for less than one year or normal operating cycle, if longer, for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

+ References

No definition available.

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- Definition

Amount of liability recognized arising from contingent consideration in a business combination, expected to be settled within one year or the normal operating cycle, if longer.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 30

-Section 25

-Paragraph 6

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Amount of liability recognized arising from contingent consideration in a business combination, expected to be settled beyond one year or the normal operating cycle, if longer.

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- Definition

Amount after tax of reclassification adjustment from accumulated other comprehensive income for unrealized gain (loss) realized upon the sale of available-for-sale securities.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

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-Subparagraph (d)

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- Definition

The cumulative amount of credit losses recognized in earnings related to debt securities held for which a portion of an other than temporary impairment (OTTI) was recognized in other comprehensive income (a component of shareholders' equity).

+ References

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