Summary of Significant Accounting Policies - Additional Information (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Sep. 30, 2018 Segment	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jan. 01, 2018 USD ($)	Dec. 31, 2017 USD ($)
Significant Accounting Policies [Line Items]
Contract with customer, liability	$ 4,600					$ 5,600
Advisory revenues	50,570	$ 86,769
Provision for doubtful accounts	$ 300	0
Depreciation and amortization of property and equipment	Depreciation is computed using the straight-line method over the life of the assets. Amortization of leasehold improvements is computed using the straight-line method over the lesser of the life of the asset or the remaining term of the lease.
Operating lease right-of-use asset	$ 34,879
Operating lease obligations	$ 37,896
Number of business segments | Segment			1
Minimum
Significant Accounting Policies [Line Items]
Amortization period of deferred cash retention awards	3 years
Maximum
Significant Accounting Policies [Line Items]
Amortization period of deferred cash retention awards	5 years
Revenue | Maximum
Significant Accounting Policies [Line Items]
Percent of revenues	1.00%
Equipment
Significant Accounting Policies [Line Items]
Estimated useful lives of fixed assets (in years)	5 years
Furniture and Fixtures
Significant Accounting Policies [Line Items]
Estimated useful lives of fixed assets (in years)	7 years
Leasehold Improvements
Significant Accounting Policies [Line Items]
Estimated useful lives of fixed assets (in years)	10 years
Estimated useful lives of fixed assets, maximum (in years)			Lesser of 10 years or the remaining lease term
Restricted Stock | Minimum
Significant Accounting Policies [Line Items]
Restricted stock units, amortization service period (years)	3 years
Restricted Stock | Maximum
Significant Accounting Policies [Line Items]
Restricted stock units, amortization service period (years)	5 years
Capital advisory engagements
Significant Accounting Policies [Line Items]
Contract with customer, liability, revenue recognized	$ 2,400	100
Interest income	200	200
Accounting Standards Update 2016-02
Significant Accounting Policies [Line Items]
Operating lease right-of-use asset				$ 38,100
Operating lease obligations				38,100
Deferred rent				$ (3,200)
Primary Capital Advisory Engagements
Significant Accounting Policies [Line Items]
Long term receivables related to private equity and real estate capital advisory engagements	$ 18,000				$ 20,000
Installments period (in years)	3 years
Reimbursement Revenue [Member]
Significant Accounting Policies [Line Items]
Advisory revenues	$ 1,000	$ 1,200
Retained Earnings
Significant Accounting Policies [Line Items]
Cumulative effect of the change in accounting principle related to revenue recognition					$ 0		$ (7,645)
Retained Earnings | Accounting Standards Update 2014-09
Significant Accounting Policies [Line Items]
Cumulative effect of the change in accounting principle related to revenue recognition						$ (7,600)