Significant Accounting Policies - Summary of Post-Trade Services Revenue by Timing of Recognition (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Significant Accounting Policies [Line Items]
Revenues	$ 176,334	$ 184,795	$ 371,798	$ 353,773
Post-trade Services [Member]
Significant Accounting Policies [Line Items]
Revenues	9,848	4,054	20,109	8,207
Post-trade Services [Member] | Transferred over Time [Member]
Significant Accounting Policies [Line Items]
Revenues	$ 9,848	3,948	20,100	8,098
Post-trade Services [Member] | Transferred at a Point in Time [Member]
Significant Accounting Policies [Line Items]
Revenues		$ 106	$ 9	$ 109