Fair Value - Schedule of Net Gains on Sales of Loans (Detail) - USD ($) $ in Thousands	1 Months Ended	11 Months Ended	12 Months Ended
	Feb. 09, 2018	Dec. 31, 2018	Dec. 31, 2017
Components of Net Gains on Sales of Loans [Line Items]
Realized gains (losses) on sales of loans	$ 3,582	$ (5,602)	$ 171,537
Change in unrealized gains (losses) on loans held for sale	(9,343)	7,425	10,309
Capitalized servicing rights	13,227	155,989	132,581
Provision for repurchases	(729)	(5,522)	(6,991)
Interest income	2,298	23,790	34,126
Other	156	(140)	(128)
Net gains on sales of loans	27,963	161,710	284,391
Interest Rate Lock Commitments [Member]
Components of Net Gains on Sales of Loans [Line Items]
Gains (losses) on derivative instruments	(4,926)	(5,089)	(22,632)
Forward Sales Commitments [Member]
Components of Net Gains on Sales of Loans [Line Items]
Gains (losses) on derivative instruments	24,570	(22,948)	(31,662)
MBS Purchase Commitments [Member]
Components of Net Gains on Sales of Loans [Line Items]
Gains (losses) on derivative instruments	$ (872)	$ 13,807	$ (2,749)