Fair value measurements - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2014
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	144,219	144,219
Investments with other-than-temporary impairment	0	0
Accrued Expenses and Other Current Liabilities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fair value of contingent consideration obligations	$ 462	$ 462
Minimum [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Milestone achievement period		2015
Milestone discount rates		11.00%
Maximum [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Milestone achievement period		2026
Milestone discount rates		15.00%
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	53	53
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	8	8