Fair Value Measurements - Fair Value Liabilities Measured on Recurring Basis (Detail) - Fair Value, Inputs, Level 3 [Member] $ in Thousands	6 Months Ended
Jun. 30, 2018 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Additions	$ 43,500
Fair value adjustments	1,500
Contingent consideration obligation, Ending Balance	$ 45,000

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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