FAIR VALUE MEASUREMENTS - Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024		Mar. 31, 2024	Dec. 31, 2023
Loans
Mortgage servicing rights	$ 3,272,902	$ 2,909,134		$ 2,651,279	$ 2,122,196
Derivative assets
Interest rate swaps	67,257	225,351	[1]
Liabilities
Participations issued	1,748,273	1,154,816	[1]
U.S. Treasury securities sold, not yet purchased	2,519,125	2,470,629	[1]
Derivative liabilities
Interest rate swaps	18,455	7,212
Residential mortgage loans
Loans
Residential mortgage loans	28,324,836	25,520,090
Fair Value, Measurements, Recurring
Assets
Agency mortgage-backed securities	68,329,720	67,434,068
Credit risk transfer securities	521,059	754,915
Loans
Mortgage servicing rights	3,272,902	2,909,134
Derivative assets
Other derivatives	59,245	204,125
Total assets	102,026,359	98,411,022
Liabilities
Debt issued by securitization vehicles	21,802,193	19,540,678
Participations issued	1,748,273	1,154,816
U.S. Treasury securities sold, not yet purchased	2,519,125	2,470,629
Derivative liabilities
Interest rate swaps	18,455	7,212
Other derivatives	162,610	52,374
Total liabilities	26,250,656	23,225,709
Fair Value, Measurements, Recurring | Assets transferred or pledged to securitization vehicles
Loans
Assets transferred or pledged to securitization vehicles	24,464,281	21,973,188
Fair Value, Measurements, Recurring | Non-Agency mortgage-backed securities
Assets
Mortgage-backed securities	1,451,524	1,493,186
Fair Value, Measurements, Recurring | Commercial mortgage-backed securities
Assets
Mortgage-backed securities	59,061	74,278
Fair Value, Measurements, Recurring | Residential mortgage loans
Loans
Residential mortgage loans	3,860,555	3,546,902
Fair Value, Measurements, Recurring | Interest rate swaps
Derivative assets
Interest rate swaps	8,012	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	5,597	190,980
Total assets	5,597	190,980
Liabilities
Debt issued by securitization vehicles	0	0
Participations issued	0	0
U.S. Treasury securities sold, not yet purchased	2,519,125	2,470,629
Derivative liabilities
Interest rate swaps	0	0
Other derivatives	148,371	16,650
Total liabilities	2,667,496	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
Mortgage-backed securities	0	0
Fair Value, Measurements, Recurring | Level 1 | Commercial mortgage-backed securities
Assets
Mortgage-backed securities	0	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	68,329,720	67,434,068
Credit risk transfer securities	521,059	754,915
Loans
Mortgage servicing rights	0	0
Derivative assets
Other derivatives	53,648	13,145
Total assets	98,747,860	95,310,908
Liabilities
Debt issued by securitization vehicles	21,802,193	19,540,678
Participations issued	1,748,273	1,154,816
U.S. Treasury securities sold, not yet purchased	0	0
Derivative liabilities
Interest rate swaps	18,455	7,212
Other derivatives	14,239	35,724
Total liabilities	23,583,160	20,738,430
Fair Value, Measurements, Recurring | Level 2 | Assets transferred or pledged to securitization vehicles
Loans
Assets transferred or pledged to securitization vehicles	24,464,281	21,973,188
Fair Value, Measurements, Recurring | Level 2 | Non-Agency mortgage-backed securities
Assets
Mortgage-backed securities	1,451,524	1,493,186
Fair Value, Measurements, Recurring | Level 2 | Commercial mortgage-backed securities
Assets
Mortgage-backed securities	59,061	74,278
Fair Value, Measurements, Recurring | Level 2 | Residential mortgage loans
Loans
Residential mortgage loans	3,860,555	3,546,902
Fair Value, Measurements, Recurring | Level 2 | Interest rate swaps
Derivative assets
Interest rate swaps	8,012	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	3,272,902	2,909,134
Derivative assets
Other derivatives	0	0
Total assets	3,272,902	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
Mortgage-backed securities	0	0
Fair Value, Measurements, Recurring | Level 3 | Commercial mortgage-backed securities
Assets
Mortgage-backed securities	0	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.