Segment Data - Balance Sheet (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Assets:
Cash and cash equivalents	$ 254,567		$ 563,217
Restricted cash	106,009		158,945
Loans held-for-investment, net	12,763,372		11,087,073
Loans held-for-sale	961,677		1,052,835
Investment securities	673,566		736,658
Properties, net	2,243,569		2,271,153
Intangible assets	65,193		70,117
Investment in unconsolidated entities	96,789		108,054
Goodwill	259,846		259,846
Derivative assets	35,615		40,555
Accrued interest receivable	113,800		95,980
Other assets	241,503		190,748
Total Assets	81,309,302		80,873,509
Liabilities:
Accounts payable, accrued expenses and other liabilities	182,226		206,845
Related-party payable	26,431		39,170
Dividends payable	139,457		137,959
Derivative liabilities	33,061		41,324
Secured financing agreements, net	9,932,662		10,146,190
Collateralized loan obligations, net	2,404,672		930,554
Unsecured senior notes, net	1,737,383		1,732,520
Total Liabilities	76,457,602		76,010,933
Starwood Property Trust, Inc. Stockholders’ Equity:
Common stock	2,952		2,921
Additional paid-in capital	5,248,490		5,209,739
Treasury stock	(138,022)		(138,022)
Accumulated other comprehensive income (loss)	41,310		43,993
Retained earnings (accumulated deficit)	(677,375)		(629,733)
Total Starwood Property Trust, Inc. Stockholders’ Equity	4,477,355		4,488,898
Non-controlling interests in consolidated subsidiaries	374,345		373,678
Total Equity	4,851,700	$ 4,854,785	4,862,576	$ 4,864,796	$ 4,817,351	$ 5,137,014
Total Liabilities and Equity	81,309,302		80,873,509
Infrastructure Lending Segment
Assets:
Goodwill	119,400		119,400
Investing and Servicing Segment
Assets:
Goodwill	140,400		140,400
Operating Segments and Corporate
Assets:
Cash and cash equivalents	253,956		562,445
Restricted cash	106,009		158,945
Loans held-for-investment, net	12,763,372		11,087,073
Loans held-for-sale	961,677		1,052,835
Investment securities	2,130,402		2,162,228
Properties, net	2,243,569		2,271,153
Intangible assets	107,271		111,493
Investment in unconsolidated entities	111,441		124,166
Goodwill	259,846		259,846
Derivative assets	35,615		40,555
Accrued interest receivable	113,919		96,114
Other assets	241,490		190,755
Total Assets	19,328,567		18,117,608
Liabilities:
Accounts payable, accrued expenses and other liabilities	182,173		206,770
Related-party payable	26,393		39,170
Dividends payable	139,457		137,959
Derivative liabilities	33,061		41,324
Secured financing agreements, net	9,954,412		10,168,190
Collateralized loan obligations, net	2,404,672		930,554
Unsecured senior notes, net	1,737,383		1,732,520
Total Liabilities	14,477,551		13,256,487
Starwood Property Trust, Inc. Stockholders’ Equity:
Common stock	2,952		2,921
Additional paid-in capital	5,248,490		5,209,739
Treasury stock	(138,022)		(138,022)
Accumulated other comprehensive income (loss)	41,310		43,993
Retained earnings (accumulated deficit)	(677,375)		(629,733)
Total Starwood Property Trust, Inc. Stockholders’ Equity	4,477,355		4,488,898
Non-controlling interests in consolidated subsidiaries	373,661		372,223
Total Equity	4,851,016		4,861,121
Total Liabilities and Equity	19,328,567		18,117,608
Operating segment | Commercial and Residential Lending Segment
Assets:
Cash and cash equivalents	60,651		160,007
Restricted cash	60,416		93,445
Loans held-for-investment, net	11,068,406		9,673,625
Loans held-for-sale	494,113		841,963
Investment securities	951,036		1,014,402
Properties, net	124,916		103,896
Intangible assets	0		0
Investment in unconsolidated entities	43,717		54,407
Goodwill	0		0
Derivative assets	12,472		6,595
Accrued interest receivable	102,086		87,922
Other assets	81,621		61,638
Total Assets	12,999,434		12,097,900
Liabilities:
Accounts payable, accrued expenses and other liabilities	38,973		41,104
Related-party payable	0		0
Dividends payable	0		0
Derivative liabilities	31,530		39,082
Secured financing agreements, net	5,751,375		5,893,999
Collateralized loan obligations, net	2,000,073		930,554
Unsecured senior notes, net	0		0
Total Liabilities	7,821,951		6,904,739
Starwood Property Trust, Inc. Stockholders’ Equity:
Common stock	0		0
Additional paid-in capital	878,471		1,192,584
Treasury stock	0		0
Accumulated other comprehensive income (loss)	41,310		44,057
Retained earnings (accumulated deficit)	4,257,587		3,956,405
Total Starwood Property Trust, Inc. Stockholders’ Equity	5,177,368		5,193,046
Non-controlling interests in consolidated subsidiaries	115		115
Total Equity	5,177,483		5,193,161
Total Liabilities and Equity	12,999,434		12,097,900
Operating segment | Infrastructure Lending Segment
Assets:
Cash and cash equivalents	31,695		4,440
Restricted cash	25,840		45,113
Loans held-for-investment, net	1,694,109		1,412,440
Loans held-for-sale	85,875		120,540
Investment securities	33,881		35,681
Properties, net	0		0
Intangible assets	0		0
Investment in unconsolidated entities	24,770		25,095
Goodwill	119,409		119,409
Derivative assets	0		0
Accrued interest receivable	5,307		2,091
Other assets	11,497		4,531
Total Assets	2,032,383		1,769,340
Liabilities:
Accounts payable, accrued expenses and other liabilities	8,464		12,144
Related-party payable	0		0
Dividends payable	0		0
Derivative liabilities	1,118		1,718
Secured financing agreements, net	957,605		1,240,763
Collateralized loan obligations, net	404,599		0
Unsecured senior notes, net	0		0
Total Liabilities	1,371,786		1,254,625
Starwood Property Trust, Inc. Stockholders’ Equity:
Common stock	0		0
Additional paid-in capital	629,130		496,387
Treasury stock	0		0
Accumulated other comprehensive income (loss)	0		0
Retained earnings (accumulated deficit)	31,467		18,328
Total Starwood Property Trust, Inc. Stockholders’ Equity	660,597		514,715
Non-controlling interests in consolidated subsidiaries	0		0
Total Equity	660,597		514,715
Total Liabilities and Equity	2,032,383		1,769,340
Operating segment | Property Segment
Assets:
Cash and cash equivalents	28,088		32,080
Restricted cash	6,681		7,192
Loans held-for-investment, net	0		0
Loans held-for-sale	0		0
Investment securities	0		0
Properties, net	1,941,500		1,969,414
Intangible assets	37,361		40,370
Investment in unconsolidated entities	0		0
Goodwill	0		0
Derivative assets	124		41
Accrued interest receivable	0		0
Other assets	91,158		69,859
Total Assets	2,104,912		2,118,956
Liabilities:
Accounts payable, accrued expenses and other liabilities	45,231		43,630
Related-party payable	0		0
Dividends payable	0		0
Derivative liabilities	0		0
Secured financing agreements, net	1,872,043		1,794,609
Collateralized loan obligations, net	0		0
Unsecured senior notes, net	0		0
Total Liabilities	1,917,274		1,838,239
Starwood Property Trust, Inc. Stockholders’ Equity:
Common stock	0		0
Additional paid-in capital	16,967		98,882
Treasury stock	0		0
Accumulated other comprehensive income (loss)	0		0
Retained earnings (accumulated deficit)	(47,694)		(44,832)
Total Starwood Property Trust, Inc. Stockholders’ Equity	(30,727)		54,050
Non-controlling interests in consolidated subsidiaries	218,365		226,667
Total Equity	187,638		280,717
Total Liabilities and Equity	2,104,912		2,118,956
Operating segment | Investing and Servicing Segment
Assets:
Cash and cash equivalents	22,618		19,546
Restricted cash	13,072		13,195
Loans held-for-investment, net	857		1,008
Loans held-for-sale	381,689		90,332
Investment securities	1,145,485		1,112,145
Properties, net	177,153		197,843
Intangible assets	69,910		71,123
Investment in unconsolidated entities	42,954		44,664
Goodwill	140,437		140,437
Derivative assets	92		147
Accrued interest receivable	495		123
Other assets	42,237		44,579
Total Assets	2,036,999		1,735,142
Liabilities:
Accounts payable, accrued expenses and other liabilities	40,245		45,309
Related-party payable	0		5
Dividends payable	0		0
Derivative liabilities	413		524
Secured financing agreements, net	742,811		606,100
Collateralized loan obligations, net	0		0
Unsecured senior notes, net	0		0
Total Liabilities	783,469		651,938
Starwood Property Trust, Inc. Stockholders’ Equity:
Common stock	0		0
Additional paid-in capital	(218,645)		(322,992)
Treasury stock	0		0
Accumulated other comprehensive income (loss)	0		(64)
Retained earnings (accumulated deficit)	1,316,994		1,260,819
Total Starwood Property Trust, Inc. Stockholders’ Equity	1,098,349		937,763
Non-controlling interests in consolidated subsidiaries	155,181		145,441
Total Equity	1,253,530		1,083,204
Total Liabilities and Equity	2,036,999		1,735,142
Corporate
Assets:
Cash and cash equivalents	110,904		346,372
Restricted cash	0		0
Loans held-for-investment, net	0		0
Loans held-for-sale	0		0
Investment securities	0		0
Properties, net	0		0
Intangible assets	0		0
Investment in unconsolidated entities	0		0
Goodwill	0		0
Derivative assets	22,927		33,772
Accrued interest receivable	6,031		5,978
Other assets	14,977		10,148
Total Assets	154,839		396,270
Liabilities:
Accounts payable, accrued expenses and other liabilities	49,260		64,583
Related-party payable	26,393		39,165
Dividends payable	139,457		137,959
Derivative liabilities	0		0
Secured financing agreements, net	630,578		632,719
Collateralized loan obligations, net	0		0
Unsecured senior notes, net	1,737,383		1,732,520
Total Liabilities	2,583,071		2,606,946
Starwood Property Trust, Inc. Stockholders’ Equity:
Common stock	2,952		2,921
Additional paid-in capital	3,942,567		3,744,878
Treasury stock	(138,022)		(138,022)
Accumulated other comprehensive income (loss)	0		0
Retained earnings (accumulated deficit)	(6,235,729)		(5,820,453)
Total Starwood Property Trust, Inc. Stockholders’ Equity	(2,428,232)		(2,210,676)
Non-controlling interests in consolidated subsidiaries	0		0
Total Equity	(2,428,232)		(2,210,676)
Total Liabilities and Equity	154,839		396,270
Securitization VIEs
Assets:
Cash and cash equivalents	611		772
Restricted cash	0		0
Loans held-for-investment, net	0		0
Loans held-for-sale	0		0
Investment securities	(1,456,836)		(1,425,570)
Properties, net	0		0
Intangible assets	(42,078)		(41,376)
Investment in unconsolidated entities	(14,652)		(16,112)
Goodwill	0		0
Derivative assets	0		0
Accrued interest receivable	(119)		(134)
Other assets	13		(7)
Total Assets	61,980,735		62,755,901
Liabilities:
Accounts payable, accrued expenses and other liabilities	53		75
Related-party payable	38		0
Dividends payable	0		0
Derivative liabilities	0		0
Secured financing agreements, net	(21,750)		(22,000)
Collateralized loan obligations, net	0		0
Unsecured senior notes, net	0		0
Total Liabilities	61,980,051		62,754,446
Starwood Property Trust, Inc. Stockholders’ Equity:
Common stock	0		0
Additional paid-in capital	0		0
Treasury stock	0		0
Accumulated other comprehensive income (loss)	0		0
Retained earnings (accumulated deficit)	0		0
Total Starwood Property Trust, Inc. Stockholders’ Equity	0		0
Non-controlling interests in consolidated subsidiaries	684		1,455
Total Equity	684		1,455
Total Liabilities and Equity	61,980,735		62,755,901
Primary beneficiary
Assets:
Total Assets	63,493,796		64,238,328
Liabilities:
Total Liabilities	62,001,710		62,776,371
Primary beneficiary | Operating Segments and Corporate
Assets:
Total Assets	0		0
Liabilities:
Total Liabilities	0		0
Primary beneficiary | Operating segment | Commercial and Residential Lending Segment
Assets:
Total Assets	0		0
Liabilities:
Total Liabilities	0		0
Primary beneficiary | Operating segment | Infrastructure Lending Segment
Assets:
Total Assets	0		0
Liabilities:
Total Liabilities	0		0
Primary beneficiary | Operating segment | Property Segment
Assets:
Total Assets	0		0
Liabilities:
Total Liabilities	0		0
Primary beneficiary | Operating segment | Investing and Servicing Segment
Assets:
Total Assets	0		0
Liabilities:
Total Liabilities	0		0
Primary beneficiary | Corporate
Assets:
Total Assets	0		0
Liabilities:
Total Liabilities	0		0
Primary beneficiary | Securitization VIEs
Assets:
Total Assets	63,493,796		64,238,328
Liabilities:
Total Liabilities	$ 62,001,710		$ 62,776,371