Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Jan. 01, 2018
Summary Of Significant Accounting Policies [Line Items]
Accumulated deficit	$ 38,296	$ (41,487)
Accounts receivable and unbilled, net	140,189	133,449
Deferred income tax liability	5,578	439
Accrued expenses	102,535	87,493
Advanced billings	$ 169,529	$ 147,935
ASU 2014-09 | Impact of Adoption of ASC 606 - Adjustments
Summary Of Significant Accounting Policies [Line Items]
Accumulated deficit			$ 5,700
Accounts receivable and unbilled, net			23,900
Deferred income tax liability			(1,600)
Accrued expenses			35,100
Pre-funded study costs			(57,400)
Advanced billings			$ 38,900