FAIR VALUE MEASUREMENTS - Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands		Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022		Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021
Assets
Mortgage-backed securities	[1]	$ 71,202,461		$ 65,789,907	[2]
Loans
Mortgage servicing rights		2,018,896	$ 1,790,980	1,748,209		$ 1,421,420	$ 1,108,937	$ 544,562
Derivative assets
Interest rate swaps		457,119		342,064	[2]
Liabilities
Participations issued		492,307		800,849	[2]
Derivative liabilities
Interest rate swaps		96,618		108,724
Residential mortgage loans
Loans
Residential mortgage loans		12,472,739		10,931,744
Fair Value, Measurements, Recurring
Assets
Agency mortgage-backed securities		67,764,264		62,274,895
Credit risk transfer securities		1,064,401		997,557
Loans
Mortgage servicing rights		2,018,896		1,748,209
Derivative assets
Other derivatives		427,093		309,058
Total assets		86,151,215		78,811,924
Liabilities
Debt issued by securitization vehicles		9,789,282		7,744,160
Participations issued		492,307		800,849
Derivative liabilities
Interest rate swaps		96,618		108,724
Other derivatives		59,564		95,448
Total liabilities		10,437,771		8,749,181
Fair Value, Measurements, Recurring | Assets transferred or pledged to securitization vehicles
Loans
Assets transferred or pledged to securitization vehicles		11,318,419		9,121,912
Fair Value, Measurements, Recurring | Non-Agency mortgage-backed securities
Assets
Mortgage-backed securities		2,008,106		1,991,146
Fair Value, Measurements, Recurring | Commercial mortgage-backed securities
Assets
Mortgage-backed securities		365,690		526,309
Fair Value, Measurements, Recurring | Residential mortgage loans
Loans
Residential mortgage loans		1,154,320		1,809,832
Fair Value, Measurements, Recurring | Interest rate swaps
Derivative assets
Interest rate swaps		30,026		33,006
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		139,108		33,179
Total assets		139,108		33,179
Liabilities
Debt issued by securitization vehicles		0		0
Participations issued		0		0
Derivative liabilities
Interest rate swaps		0		0
Other derivatives		37,049		11,919
Total liabilities		37,049		11,919
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		67,764,264		62,274,895
Credit risk transfer securities		1,064,401		997,557
Loans
Mortgage servicing rights		0		0
Derivative assets
Other derivatives		287,985		275,879
Total assets		83,993,211		77,030,536
Liabilities
Debt issued by securitization vehicles		9,789,282		7,744,160
Participations issued		492,307		800,849
Derivative liabilities
Interest rate swaps		96,618		108,724
Other derivatives		22,515		83,529
Total liabilities		10,400,722		8,737,262
Fair Value, Measurements, Recurring | Level 2 | Assets transferred or pledged to securitization vehicles
Loans
Assets transferred or pledged to securitization vehicles		11,318,419		9,121,912
Fair Value, Measurements, Recurring | Level 2 | Non-Agency mortgage-backed securities
Assets
Mortgage-backed securities		2,008,106		1,991,146
Fair Value, Measurements, Recurring | Level 2 | Commercial mortgage-backed securities
Assets
Mortgage-backed securities		365,690		526,309
Fair Value, Measurements, Recurring | Level 2 | Residential mortgage loans
Loans
Residential mortgage loans		1,154,320		1,809,832
Fair Value, Measurements, Recurring | Level 2 | Interest rate swaps
Derivative assets
Interest rate swaps		30,026		33,006
Fair Value, Measurements, Recurring | Level 3
Assets
Agency mortgage-backed securities		0		0
Credit risk transfer securities		0		0
Loans
Mortgage servicing rights		2,018,896		1,748,209
Derivative assets
Other derivatives		0		0
Total assets		2,018,896		1,748,209
Liabilities
Debt issued by securitization vehicles		0		0
Participations issued		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] (3)Excludes $1.3 billion and $1.0 billion at June 30, 2023 and December 31, 2022, respectively, of non-Agency mortgage-backed securities in consolidated VIEs pledged as collateral and eliminated from the Company’s Consolidated Statements of Financial Condition. 

[2] (1)Derived from the audited consolidated financial statements at December 31, 2022.