Loans Held for Sale - Schedule of Summarizes The Notional Amounts For Interest Rate Lock Commitments And Best Efforts Forward Trades Pertaining To Loans Held For Sale (Detail) - Loans Held for Sale [Member] - USD ($) $ in Thousands	Mar. 31, 2020	Mar. 31, 2019
Loans Held For Sale [Line Items]
Total derivative instruments	$ 887,675	$ 234,917
Interest Rate Lock Commitments [Member]
Loans Held For Sale [Line Items]
Total derivative instruments	389,387	85,802
Best Efforts Forward Trades [Member]
Loans Held For Sale [Line Items]
Total derivative instruments	152,788	92,115
MBS Forward Trades [Member]
Loans Held For Sale [Line Items]
Total derivative instruments	$ 345,500	$ 57,000