Fair Value Measurements - Summary of Change in Fair Value of Contingent Consideration as Determined by Level 3 Inputs (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 43,740
Change in fair value	2,100	3,140
Ending balance	45,840
Level 3 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	43,740
Payments	0
Change in fair value	2,100
Ending balance	$ 45,840