Freestanding Derivative Financial Instruments - Schedule of Notional or Contractual Amounts and Fair Values of Derivative Instruments (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Derivative Assets	$ 18,387	$ 29,394
Derivative Liabilities	13,737	1,250
Derivative Assets, Cash Margin	12,087	0
Derivative Liabilities, Cash Margin	0	1,533
Interest Rate Lock Commitments [Member]
Derivative [Line Items]
Notional/ Contractual Amount	1,303,501	1,509,712
Derivative Assets	16,617	26,637
Derivative Liabilities	327	269
Forward Sales Commitments [Member]
Derivative [Line Items]
Notional/ Contractual Amount	2,300,606	1,724,500
Derivative Assets	388	2,224
Derivative Liabilities	13,359	903
MBS Purchase Commitments [Member]
Derivative [Line Items]
Notional/ Contractual Amount	677,500	298,000
Derivative Assets	1,382	533
Derivative Liabilities	$ 51	$ 78