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Income taxes.

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Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2017
Accounting Policies [Line Items]
Account receivables	$ 26,738	$ 9,586
Interest Income	653	408	$ 263
Retained earnings (accumulated deficit)	(237,782)	(139,918)
Accumulated other comprehensive income	$ (453)	1,827	(1,734)
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%
Revenue and Expense Recognition and Equity-Based Compensation
Revenue recognized	$ 4,948
Income Taxes
Unrecognized tax benefits	$ 0	0	$ 0
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
Revenue recognized	$ 4,788
Reimbursable expenses recognized	$ 16,694
ASU 2016-09 \| Adjusted \| Deferred Tax Assets
Revenue and Expense Recognition and Equity-Based Compensation
Tax effect of adjustment				$ 658
ASU 2016-09 \| Adjusted \| Retained Earnings (Accumulated Deficit)
Revenue and Expense Recognition and Equity-Based Compensation
Cumulative effect on retained earnings and APIC				(4,855)
Tax effect of adjustment				658
ASU 2016-09 \| Adjusted \| Additional Paid-in Capital
Revenue and Expense Recognition and Equity-Based Compensation
Cumulative effect on retained earnings and APIC				$ 4,855
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