Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended		12 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2017	Jan. 01, 2019	Dec. 31, 2018
Accounting Policies [Line Items]
Cash	$ 48,113		$ 42,843		$ 48,113	$ 42,843			$ 59,705
Cash equivalents	60,247		90,025		60,247	90,025			201,395
Account receivables	23,556				23,556				26,738
Interest Income	245		106		520	207
Retained earnings (accumulated deficit)	(327,353)				$ (327,353)				$ (237,782)
Accumulated other comprehensive income	(57)	$ 540	(1,843)	$ 1,679
Percentage of tax benefits payable to partners under tax receivable agreement					85.00%
Remaining percentage of cash savings realized by the Company (as a percent)					15.00%
Income Taxes
Unrecognized tax benefits	0		$ 0		$ 0	$ 0
Assets and Liabilities, Lessee
Operating Lease, Liability	54,273				54,273
Operating lease, right-of-use asset	$ 46,617				$ 46,617
Issued Prior to December 1, 2016
Revenue and Expense Recognition and Equity-Based Compensation
Minimum age of retiring employees required so that certain qualifying awards granted during employment will not be forfeited					54 years
Consecutive years of service of retiring employees required so that certain qualifying awards granted during employment will not be forfeited					8 years
Issued on or After December 1, 2016
Revenue and Expense Recognition and Equity-Based Compensation
Minimum age of retiring employees required so that certain qualifying awards granted during employment will not be forfeited					56 years
Consecutive years of service of retiring employees required so that certain qualifying awards granted during employment will not be forfeited					5 years
Minimum total age and consecutive years of service of retiring employees required so that certain qualifying awards granted during employment will not be forfeited					65 years
ASU 2016-01
Accounting Policies [Line Items]
Retained earnings (accumulated deficit)							$ (317)
Accumulated other comprehensive income							317
ASU 2014-09
Revenue and Expense Recognition and Equity-Based Compensation
Cumulative effect on retained earnings and APIC							3,722
Tax effect of adjustment							567
Net change resulting from cumulative effect on retained earnings and APIC							$ 3,155
ASU 2016-02
Assets and Liabilities, Lessee
Operating Lease, Liability								$ 63,252
Operating lease, right-of-use asset								63,252
ASU 2016-02 | Adjustment For Prepaid Rent
Assets and Liabilities, Lessee
Operating lease, right-of-use asset								1,666
ASU 2016-02 | Adjustment For Accrued Rent
Assets and Liabilities, Lessee
Operating lease, right-of-use asset								$ 7,139
Minimum
Accounting Policies [Line Items]
Installment Period					3 years
Minimum | Office Equipment and Furniture and Fixtures
Accounting Policies [Line Items]
Useful lives					3 years
Maximum
Accounting Policies [Line Items]
Installment Period					4 years
Maximum | Office Equipment and Furniture and Fixtures
Accounting Policies [Line Items]
Useful lives					7 years