Fair value measurements - Roll-Forward of Fair Value of the Company's Contingent Consideration Obligations (Detail) - Significant unobservable inputs (Level 3) [Member] - Contingent consideration obligations [Member] $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 5,230
Changes in fair value	296
Ending balance	$ 5,526