ITG Acquisition - Pro Forma Results, Narrative (Details) $ / shares in Units, $ in Millions	Mar. 01, 2019 USD ($) $ / shares
Business Acquisition [Line Items]
Advisory and other professional fees | $	$ 15.1
ITG
Business Acquisition [Line Items]
Advisory and other professional fees | $	$ 18.2
Common stock, par value (in dollars per share) | $ / shares	$ 0.01
Right to receive cash (in dollars per share) | $ / shares	$ 30.30