Commitments and Contingencies - Schedule of Principal Contractual Obligations (Parenthetical) (Detail) $ in Millions	Jun. 30, 2018 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Loan participations sold excluded from contractual obligations	$ 153.1
Non-consolidated senior interests excluded from contractual obligations	489.3
Securitized debt obligations excluded from contractual obligations	$ 1,300.0