Warehouse Lines of Credit - Summary of Line of Credit (Details) - USD ($)	Jun. 30, 2021	Dec. 31, 2020
Line of Credit Facility [Line Items]
Outstanding amount	$ 0	$ 320,300,000
Warehouse Line of Credit
Line of Credit Facility [Line Items]
Outstanding amount	11,249,213,000	6,941,397,000
Current aggregate committed amount	2,000,000,000.0
Warehouse Line of Credit | Line of Credit Due June 23, 2021
Line of Credit Facility [Line Items]
Maximum borrowing capacity	400,000,000
Outstanding amount	0	287,073,000
Warehouse Line of Credit | Line of Credit Due July 1, 2021
Line of Credit Facility [Line Items]
Maximum borrowing capacity	2,000,000,000
Outstanding amount	4,236,000	499,841,000
Warehouse Line of Credit | Line of Credit Due September 7, 2021
Line of Credit Facility [Line Items]
Maximum borrowing capacity	750,000,000
Outstanding amount	512,341,000	209,138,000
Warehouse Line of Credit | Line of Credit Due September 19, 2021
Line of Credit Facility [Line Items]
Maximum borrowing capacity	150,000,000
Outstanding amount	0	112,429,000
Warehouse Line of Credit | Line of Credit Due September 23, 2021
Line of Credit Facility [Line Items]
Maximum borrowing capacity	400,000,000
Outstanding amount	341,372,000	248,947,000
Warehouse Line of Credit | Line of Credit Due October 29, 2021
Line of Credit Facility [Line Items]
Maximum borrowing capacity	4,000,000,000
Outstanding amount	3,913,236,000	1,685,138,000
Warehouse Line of Credit | Line of Credit Due November 16, 2021
Line of Credit Facility [Line Items]
Maximum borrowing capacity	250,000,000
Outstanding amount	216,464,000	249,006,000
Warehouse Line of Credit | Line of Credit Due December 23, 2021
Line of Credit Facility [Line Items]
Maximum borrowing capacity	250,000,000
Outstanding amount	140,817,000	86,928,000
Warehouse Line of Credit | Line of Credit Due December 28, 2021
Line of Credit Facility [Line Items]
Maximum borrowing capacity	500,000,000
Outstanding amount	407,046,000	365,577,000
Warehouse Line of Credit | Line of Credit Due January 10, 2022
Line of Credit Facility [Line Items]
Maximum borrowing capacity	1,000,000,000
Outstanding amount	884,839,000	769,510,000
Warehouse Line of Credit | Line of Credit Due February 23, 2022
Line of Credit Facility [Line Items]
Maximum borrowing capacity	3,000,000,000
Outstanding amount	1,949,239,000	1,344,851,000
Warehouse Line of Credit | Line of Credit Due March 4, 2022
Line of Credit Facility [Line Items]
Maximum borrowing capacity	500,000,000
Outstanding amount	318,599,000	666,891,000
Warehouse Line of Credit | Line of Credit Due May 24, 2022
Line of Credit Facility [Line Items]
Maximum borrowing capacity	150,000,000
Outstanding amount	143,178,000	140,237,000
Warehouse Line of Credit | Line of Credit Due July 6, 2022
Line of Credit Facility [Line Items]
Maximum borrowing capacity	200,000,000
Outstanding amount	181,159,000	198,705,000
Warehouse Line of Credit | Line of Credit Due April 23, 2023
Line of Credit Facility [Line Items]
Maximum borrowing capacity	1,000,000
Outstanding amount	595,554,000	0
Warehouse Line of Credit | Line of Credit Due May 26, 2023
Line of Credit Facility [Line Items]
Maximum borrowing capacity	2,000,000
Outstanding amount	1,640,971,000	1,179,000
Warehouse Line of Credit | Line of Credit, ASAP program
Line of Credit Facility [Line Items]
Maximum borrowing capacity	250,000,000
Outstanding amount	162,000	75,947,000
Warehouse Line of Credit | Line of Credit, Gestation line
Line of Credit Facility [Line Items]
Maximum borrowing capacity	150,000,000.0
Outstanding amount	$ 0	$ 0