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Acquisitions - Additional Information (Detail) - USD ($) $ in Thousands			6 Months Ended	12 Months Ended
	Jan. 31, 2019	Nov. 15, 2018	Jun. 30, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Total consideration transferred			$ 102,300	$ 94,200
Business acquisition, contingent cash consideration				18,000
Additional goodwill recognized			55,872	$ 39,700
Measurement period adjustments			$ 1,100
Poten & Partners Group [Member]
Business Acquisition [Line Items]
Business acquisition date		Nov. 15, 2018
Ed Broking Group Limited [Member]
Business Acquisition [Line Items]
Business acquisition date	Jan. 31, 2019