FAIR VALUE MEASUREMENTS - Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Mar. 31, 2025	Dec. 31, 2024		Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023
Loans
Mortgage servicing rights	$ 3,281,190	$ 3,272,902	$ 2,909,134		$ 2,785,614	$ 2,651,279	$ 2,122,196
Derivative assets
Interest rate swaps	149,690		225,351	[1]
Liabilities
Participations issued	1,556,900		1,154,816	[1]
U.S. Treasury securities sold, not yet purchased	2,528,167		2,470,629	[1]
Derivative liabilities
Interest rate swaps	23,547		7,212
Residential mortgage loans
Loans
Residential mortgage loans	30,744,062		25,520,090
Fair Value, Measurements, Recurring
Assets
Agency mortgage-backed securities	71,756,638		67,434,068
Credit risk transfer securities	414,047		754,915
Loans
Mortgage servicing rights	3,281,190		2,909,134
Derivative assets
Other derivatives	144,687		204,125
Total assets	107,675,568		98,411,022
Liabilities
Debt issued by securitization vehicles	24,107,249		19,540,678
Participations issued	1,556,900		1,154,816
U.S. Treasury securities sold, not yet purchased	2,528,167		2,470,629
Derivative liabilities
Interest rate swaps	23,547		7,212
Other derivatives	402,446		52,374
Total liabilities	28,618,309		23,225,709
Fair Value, Measurements, Recurring | Assets transferred or pledged to securitization vehicles
Loans
Assets transferred or pledged to securitization vehicles	27,021,790		21,973,188
Fair Value, Measurements, Recurring | Non-Agency mortgage-backed securities
Assets
Non-Agency mortgage-backed securities	1,329,941		1,493,186
Fair Value, Measurements, Recurring | Commercial mortgage-backed securities
Assets
Non-Agency mortgage-backed securities			74,278
Fair Value, Measurements, Recurring | Residential mortgage loans
Loans
Residential mortgage loans	3,722,272		3,546,902
Fair Value, Measurements, Recurring | Interest rate swaps
Derivative assets
Interest rate swaps	5,003		21,226
Fair Value, Measurements, Recurring | Level 1
Assets
Agency mortgage-backed securities	0		0
Credit risk transfer securities	0		0
Loans
Mortgage servicing rights	0		0
Derivative assets
Other derivatives	34,258		190,980
Total assets	34,258		190,980
Liabilities
Debt issued by securitization vehicles	0		0
Participations issued	0		0
U.S. Treasury securities sold, not yet purchased	2,528,167		2,470,629
Derivative liabilities
Interest rate swaps	0		0
Other derivatives	401,113		16,650
Total liabilities	2,929,280		2,487,279
Fair Value, Measurements, Recurring | Level 1 | Assets transferred or pledged to securitization vehicles
Loans
Assets transferred or pledged to securitization vehicles	0		0
Fair Value, Measurements, Recurring | Level 1 | Non-Agency mortgage-backed securities
Assets
Non-Agency mortgage-backed securities	0		0
Fair Value, Measurements, Recurring | Level 1 | Commercial mortgage-backed securities
Assets
Non-Agency mortgage-backed securities			0
Fair Value, Measurements, Recurring | Level 1 | Residential mortgage loans
Loans
Residential mortgage loans	0		0
Fair Value, Measurements, Recurring | Level 1 | Interest rate swaps
Derivative assets
Interest rate swaps	0		0
Fair Value, Measurements, Recurring | Level 2
Assets
Agency mortgage-backed securities	71,756,638		67,434,068
Credit risk transfer securities	414,047		754,915
Loans
Mortgage servicing rights	0		0
Derivative assets
Other derivatives	110,429		13,145
Total assets	104,360,120		95,310,908
Liabilities
Debt issued by securitization vehicles	24,107,249		19,540,678
Participations issued	1,556,900		1,154,816
U.S. Treasury securities sold, not yet purchased	0		0
Derivative liabilities
Interest rate swaps	23,547		7,212
Other derivatives	1,333		35,724
Total liabilities	25,689,029		20,738,430
Fair Value, Measurements, Recurring | Level 2 | Assets transferred or pledged to securitization vehicles
Loans
Assets transferred or pledged to securitization vehicles	27,021,790		21,973,188
Fair Value, Measurements, Recurring | Level 2 | Non-Agency mortgage-backed securities
Assets
Non-Agency mortgage-backed securities	1,329,941		1,493,186
Fair Value, Measurements, Recurring | Level 2 | Commercial mortgage-backed securities
Assets
Non-Agency mortgage-backed securities			74,278
Fair Value, Measurements, Recurring | Level 2 | Residential mortgage loans
Loans
Residential mortgage loans	3,722,272		3,546,902
Fair Value, Measurements, Recurring | Level 2 | Interest rate swaps
Derivative assets
Interest rate swaps	5,003		21,226
Fair Value, Measurements, Recurring | Level 3
Assets
Agency mortgage-backed securities	0		0
Credit risk transfer securities	0		0
Loans
Mortgage servicing rights	3,281,190		2,909,134
Derivative assets
Other derivatives	0		0
Total assets	3,281,190		2,909,134
Liabilities
Debt issued by securitization vehicles	0		0
Participations issued	0		0
U.S. Treasury securities sold, not yet purchased	0		0
Derivative liabilities
Interest rate swaps	0		0
Other derivatives	0		0
Total liabilities	0		0
Fair Value, Measurements, Recurring | Level 3 | Assets transferred or pledged to securitization vehicles
Loans
Assets transferred or pledged to securitization vehicles	0		0
Fair Value, Measurements, Recurring | Level 3 | Non-Agency mortgage-backed securities
Assets
Non-Agency mortgage-backed securities	0		0
Fair Value, Measurements, Recurring | Level 3 | Commercial mortgage-backed securities
Assets
Non-Agency mortgage-backed securities			0
Fair Value, Measurements, Recurring | Level 3 | Residential mortgage loans
Loans
Residential mortgage loans	0		0
Fair Value, Measurements, Recurring | Level 3 | Interest rate swaps
Derivative assets
Interest rate swaps	$ 0		$ 0

[1] (1)Derived from the audited consolidated financial statements at December 31, 2024.