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Fair value measurements - Roll-Forward of Fair Value of the Company's Contingent Consideration Obligations (Detail) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2016
Mar. 31, 2015
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Changes in fair value $ 1,013 $ 215
Significant unobservable inputs (Level 3) [Member] | Contingent consideration obligations [Member]    
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Beginning balance 8,665  
Changes in fair value 1,013  
Ending balance $ 9,678