Fair Value - Quantitative Summary of Key Unobservable Inputs Used in Valuation of Interest Rate Lock Commitments (Detail)	Jun. 30, 2019	Dec. 31, 2018
Pull-Through Rate [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Key inputs used in valuation of IRLCs	35.70%	45.40%
Pull-Through Rate [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Key inputs used in valuation of IRLCs	100.00%	100.00%
Pull-Through Rate [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Key inputs used in valuation of IRLCs	90.90%	91.80%
Servicing Fee Multiple [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Key inputs used in valuation of IRLCs	1.80%	2.40%
Servicing Fee Multiple [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Key inputs used in valuation of IRLCs	5.80%	5.60%
Servicing Fee Multiple [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Key inputs used in valuation of IRLCs	4.50%	4.30%
Percentage of UPB [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Key inputs used in valuation of IRLCs	0.60%	0.60%
Percentage of UPB [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Key inputs used in valuation of IRLCs	2.70%	3.60%
Percentage of UPB [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Key inputs used in valuation of IRLCs	1.50%	2.20%