Fair value measurement - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Fair Value Measurements [Line Items]
Reversal of contingent consideration	$ 4,400,000	$ 8,200,000
Contingent consideration liabilities	20,829,000	33,433,000
Current portion of contingent consideration	7,291,000	11,276,000
Minimum
Fair Value Measurements [Line Items]
Fair value of contingent consideration liability associated with future milestone	7,000,000.0
Maximum
Fair Value Measurements [Line Items]
Fair value of contingent consideration liability associated with future milestone	43,800,000.0
Significant Unobservable Inputs (Level 3)
Fair Value Measurements [Line Items]
Contingent consideration liabilities	20,829,000	$ 33,433,000
Current portion of contingent consideration	7,291,000
Other liabilities	$ 13,500,000