Acquisitions (First Half 2018) - Additional Information (Detail) $ in Millions	6 Months Ended		9 Months Ended
	Jun. 30, 2018 USD ($) Business	Jun. 30, 2017 USD ($) Business	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)
Business Acquisition Contingent Consideration [Line Items]
Consideration paid in cash	$ 23.4	$ 23.7
Consideration paid in common stock	0.9	2.0
Contingent consideration	12.4	$ 17.5	$ 12.4	$ 17.5
Contingent consideration, current			3.4
Contingent consideration, non-current			9.0
Annual revenue	$ 9.1		$ 23.2
Number of businesses acquired | Business		3
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
Number of businesses acquired | Business	2
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