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], USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014
Significant unobservable inputs (Level 3) [Member] | Contingent consideration obligations [Member]
Fair Value Assets Measured On Recurring And Nonrecurring Basis [Line Items]
Beginning balance	$ 0
Additions	6,550
Changes in fair value	78
Payments	0
Ending balance	$ 6,628