Acquisitions - Additional Information (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2019 USD ($) Client_List shares	Jun. 30, 2018 USD ($) Business Client_List shares	Dec. 31, 2018 USD ($)
Business Acquisition, Contingent Consideration [Line Items]
Consideration paid in cash		$ 23,400
Contingent consideration		12,400
Contingent consideration, current	$ 18,824	3,400	$ 22,538
Contingent consideration, non-current	9,181	9,000	17,170
Annual revenue		$ 9,100
Number of businesses acquired | Business		2
Consideration paid in common stock		$ 900
Goodwill	566,009		$ 564,300
Changes in fair value of contingent consideration	(200)	3,100
Consideration paid in cash	$ 11,300	$ 4,100
Number of common stock issued | shares	98,000	56,000
Wenner Group, LLC [Member]
Business Acquisition, Contingent Consideration [Line Items]
Effective date of acquisition	Jan. 01, 2019
Acquired entity, name	Wenner Group, LLC
Consideration paid in cash	$ 1,300
Contingent consideration	1,800
Contingent consideration, current	600
Contingent consideration, non-current	1,200
Annual revenue	2,400
InR Advisory Services, LLC [Member]
Business Acquisition, Contingent Consideration [Line Items]
Effective date of acquisition		Apr. 01, 2018
Acquired entity, name		InR Advisory Services, LLC
Laurus Transaction Advisors, LLC [Member]
Business Acquisition, Contingent Consideration [Line Items]
Effective date of acquisition		Feb. 01, 2018
Acquired entity, name		Laurus Transaction Advisors, LLC
InR Advisory Services, LLC (“InR”) and Laurus Transaction Advisors, LLC (“Laurus”) [Member]
Business Acquisition, Contingent Consideration [Line Items]
Goodwill	$ 2,165	$ 32,255
Acquisition of Client Lists [Member]
Business Acquisition, Contingent Consideration [Line Items]
Number of client lists purchased | Client_List	0	0
Previous Client List Purchases [Member]
Business Acquisition, Contingent Consideration [Line Items]
Consideration paid in cash	$ 400	$ 500