Commitments and Contingencies - Schedule of Principal Debt Repayments (Parenthetical) (Detail) $ in Millions	Mar. 31, 2018 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Loan participations sold excluded from contractual obligations	$ 107.3
Non-consolidated senior interests excluded from contractual obligations	449.5
Securitized debt obligations excluded from contractual obligations	$ 1.3