Balance Sheet Detail - Accrued Expenses and Trade Payables (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Accounts Payable And Accrued Liabilities Current [Abstract]
Accrued payroll and related taxes	$ 17,626	$ 13,338
Accrued state, federal, and local taxes	1,380	1,044
Accrued referral source commissions	4,496	4,271
Trade payables	6,058	9,822
Earnout liabilities	3,000	3,061
Accrued financing costs	298	257
Accrued leasehold improvements	669	1,288
Other	7,241	5,083
Total	$ 40,768	$ 38,164