Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Jan. 01, 2018
Summary Of Significant Accounting Policies [Line Items]
Accumulated deficit	$ (13,136)	$ (41,487)
Accounts receivable and unbilled, net	129,624	133,449
Deferred income tax liability	3,435	439
Accrued expenses	82,247	87,493
Advanced billings	$ 150,243	$ 147,935
ASC 606 | 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