Other Assets and Liabilities - Summary of Components of Other Assets (Parenthetical) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Jul. 31, 2018	Jun. 30, 2017
Schedule Of Other Assets [Line Items]
Subordinate risk retention interest	$ 99.0
Percentage of yield in subordinate risk retention interest	10.00%
Single asset securitization principal amount		$ 1,000.0	$ 474.6
2018 Single Asset Securitization [Member]
Schedule Of Other Assets [Line Items]
Single asset securitization principal amount	$ 1,000.0
Single asset securitization maximum maturity date	Jun. 09, 2025