Fair Value Measurements - Schedule of Additional Information about Financial Assets and Liabilities Measured at Fair Value Utilized Level 3 (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Loans Held For Sale [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Balance, beginning of period	$ 654,733	$ 384,375
Originations	3,978,453	5,699,581
Sales	(4,300,868)	(5,652,693)
Included in earnings (or changes in net assets)	115,519	223,470
Transfers in and/or out of Level 3	0	0
Balance, end of period	447,837	654,733
The amount of total gains or losses for the period included in earnings (or changes in net assets) attributable to the change in unrealized gains or losses relating to assets still held at reporting date	0	0
Derivative Financial Assets TBA Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Balance, beginning of period	0	0
Transfers in and/or out of Level 3	3,165	0
Balance, end of period	3,165	0
The amount of total gains or losses for the period included in earnings (or changes in net assets) attributable to the change in unrealized gains or losses relating to assets still held at reporting date	0	0
Interest Rate Lock Commitments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Balance, beginning of period	32,011	4,518
Transfers in and/or out of Level 3	(19,086)	27,493
Balance, end of period	12,925	32,011
The amount of total gains or losses for the period included in earnings (or changes in net assets) attributable to the change in unrealized gains or losses relating to assets still held at reporting date	0	0
Forward Sales Commitments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Balance, beginning of period	0	0
Transfers in and/or out of Level 3	222	0
Balance, end of period	222	0
The amount of total gains or losses for the period included in earnings (or changes in net assets) attributable to the change in unrealized gains or losses relating to assets still held at reporting date	0	0
Derivative Financial Liabilities Interest Rate Lock Commitments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Balance, beginning of period	0	0
Transfers in and/or out of Level 3	130	0
Balance, end of period	130	0
The amount of total gains or losses for the period included in earnings (or changes in net assets) attributable to the change in unrealized gains or losses relating to assets still held at reporting date	$ 0	$ 0