Segment and Geographic Data - Balance sheets (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Assets:
Cash and cash equivalents	$ 351,190	$ 563,217
Restricted cash	118,724	158,945
Loans held-for-investment, net	12,321,493	11,087,073
Loans held-for-sale	844,631	1,052,835
Investment securities	678,287	736,658
Properties, net	2,244,748	2,271,153
Intangible assets	66,772	70,117
Investment in unconsolidated entities	100,907	108,054
Goodwill	259,846	259,846
Derivative assets	38,029	40,555
Accrued interest receivable	101,713	95,980
Other assets	208,873	190,748
Total Assets	79,702,323	80,873,509
Liabilities:
Accounts payable, accrued expenses and other liabilities	178,215	206,845
Related-party payable	36,135	39,170
Dividends payable	138,906	137,959
Derivative liabilities	34,805	41,324
Secured financing agreements, net	10,895,932	10,146,190
Collateralized loan obligations, net	931,178	930,554
Unsecured senior notes, net	1,735,658	1,732,520
Total Liabilities	74,847,538	76,010,933
Starwood Property Trust, Inc. Stockholders' Equity:
Common stock	2,943	2,921
Additional paid-in capital	5,225,037	5,209,739
Treasury stock	(138,022)	(138,022)
Accumulated other comprehensive income (loss)	41,654	43,993	$ 35,884	$ 50,932
Retained earnings (accumulated deficit)	(654,750)	(629,733)
Total Starwood Property Trust, Inc. Stockholders' Equity	4,476,862	4,488,898
Non-controlling interests in consolidated subsidiaries	377,923	373,678
Total Equity	4,854,785	4,862,576	$ 4,817,351	$ 5,137,014
Total Liabilities and Equity	79,702,323	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	350,406	562,445
Restricted cash	118,724	158,945
Loans held-for-investment, net	12,321,493	11,087,073
Loans held-for-sale	844,631	1,052,835
Investment securities	2,110,919	2,162,228
Properties, net	2,244,748	2,271,153
Intangible assets	109,690	111,493
Investment in unconsolidated entities	116,789	124,166
Goodwill	259,846	259,846
Derivative assets	38,029	40,555
Accrued interest receivable	101,845	96,114
Other assets	208,889	190,755
Total Assets	18,826,009	18,117,608
Liabilities:
Accounts payable, accrued expenses and other liabilities	178,124	206,770
Related-party payable	36,135	39,170
Dividends payable	138,906	137,959
Derivative liabilities	34,805	41,324
Secured financing agreements, net	10,917,775	10,168,190
Collateralized loan obligations, net	931,178	930,554
Unsecured senior notes, net	1,735,658	1,732,520
Total Liabilities	13,972,581	13,256,487
Starwood Property Trust, Inc. Stockholders' Equity:
Common stock	2,943	2,921
Additional paid-in capital	5,225,037	5,209,739
Treasury stock	(138,022)	(138,022)
Accumulated other comprehensive income (loss)	41,654	43,993
Retained earnings (accumulated deficit)	(654,750)	(629,733)
Total Starwood Property Trust, Inc. Stockholders' Equity	4,476,862	4,488,898
Non-controlling interests in consolidated subsidiaries	376,566	372,223
Total Equity	4,853,428	4,861,121
Total Liabilities and Equity	18,826,009	18,117,608
Operating segment | Commercial and Residential Lending Segment
Assets:
Cash and cash equivalents	56,629	160,007
Restricted cash	69,882	93,445
Loans held-for-investment, net	10,733,752	9,673,625
Loans held-for-sale	587,037	841,963
Investment securities	969,968	1,014,402
Properties, net	93,718	103,896
Investment in unconsolidated entities	47,514	54,407
Derivative assets	13,088	6,595
Accrued interest receivable	97,853	87,922
Other assets	61,677	61,638
Total Assets	12,731,118	12,097,900
Liabilities:
Accounts payable, accrued expenses and other liabilities	37,206	41,104
Derivative liabilities	33,190	39,082
Secured financing agreements, net	6,502,059	5,893,999
Collateralized loan obligations, net	931,178	930,554
Total Liabilities	7,503,633	6,904,739
Starwood Property Trust, Inc. Stockholders' Equity:
Additional paid-in capital	1,074,553	1,192,584
Accumulated other comprehensive income (loss)	41,654	44,057
Retained earnings (accumulated deficit)	4,111,160	3,956,405
Total Starwood Property Trust, Inc. Stockholders' Equity	5,227,367	5,193,046
Non-controlling interests in consolidated subsidiaries	118	115
Total Equity	5,227,485	5,193,161
Total Liabilities and Equity	12,731,118	12,097,900
Operating segment | Infrastructure Lending Segment
Assets:
Cash and cash equivalents	7,873	4,440
Restricted cash	27,973	45,113
Loans held-for-investment, net	1,586,808	1,412,440
Loans held-for-sale	89,368	120,540
Investment securities	34,951	35,681
Investment in unconsolidated entities	24,840	25,095
Goodwill	119,409	119,409
Accrued interest receivable	3,310	2,091
Other assets	7,107	4,531
Total Assets	1,901,639	1,769,340
Liabilities:
Accounts payable, accrued expenses and other liabilities	16,010	12,144
Derivative liabilities	1,310	1,718
Secured financing agreements, net	1,259,813	1,240,763
Total Liabilities	1,277,133	1,254,625
Starwood Property Trust, Inc. Stockholders' Equity:
Additional paid-in capital	599,666	496,387
Retained earnings (accumulated deficit)	24,840	18,328
Total Starwood Property Trust, Inc. Stockholders' Equity	624,506	514,715
Total Equity	624,506	514,715
Total Liabilities and Equity	1,901,639	1,769,340
Operating segment | Property Segment
Assets:
Cash and cash equivalents	39,791	32,080
Restricted cash	6,672	7,192
Properties, net	1,954,880	1,969,414
Intangible assets	38,833	40,370
Derivative assets	162	41
Other assets	85,740	69,859
Total Assets	2,126,078	2,118,956
Liabilities:
Accounts payable, accrued expenses and other liabilities	44,184	43,630
Secured financing agreements, net	1,871,026	1,794,609
Total Liabilities	1,915,210	1,838,239
Starwood Property Trust, Inc. Stockholders' Equity:
Additional paid-in capital	25,905	98,882
Retained earnings (accumulated deficit)	(40,641)	(44,832)
Total Starwood Property Trust, Inc. Stockholders' Equity	(14,736)	54,050
Non-controlling interests in consolidated subsidiaries	225,604	226,667
Total Equity	210,868	280,717
Total Liabilities and Equity	2,126,078	2,118,956
Operating segment | Investing and Servicing Segment
Assets:
Cash and cash equivalents	29,064	19,546
Restricted cash	14,197	13,195
Loans held-for-investment, net	933	1,008
Loans held-for-sale	168,226	90,332
Investment securities	1,106,000	1,112,145
Properties, net	196,150	197,843
Intangible assets	70,857	71,123
Investment in unconsolidated entities	44,435	44,664
Goodwill	140,437	140,437
Derivative assets	320	147
Accrued interest receivable	274	123
Other assets	44,719	44,579
Total Assets	1,815,612	1,735,142
Liabilities:
Accounts payable, accrued expenses and other liabilities	24,110	45,309
Related-party payable		5
Derivative liabilities	305	524
Secured financing agreements, net	653,222	606,100
Total Liabilities	677,637	651,938
Starwood Property Trust, Inc. Stockholders' Equity:
Additional paid-in capital	(298,098)	(322,992)
Accumulated other comprehensive income (loss)		(64)
Retained earnings (accumulated deficit)	1,285,229	1,260,819
Total Starwood Property Trust, Inc. Stockholders' Equity	987,131	937,763
Non-controlling interests in consolidated subsidiaries	150,844	145,441
Total Equity	1,137,975	1,083,204
Total Liabilities and Equity	1,815,612	1,735,142
Corporate
Assets:
Cash and cash equivalents	217,049	346,372
Derivative assets	24,459	33,772
Accrued interest receivable	408	5,978
Other assets	9,646	10,148
Total Assets	251,562	396,270
Liabilities:
Accounts payable, accrued expenses and other liabilities	56,614	64,583
Related-party payable	36,135	39,165
Dividends payable	138,906	137,959
Secured financing agreements, net	631,655	632,719
Unsecured senior notes, net	1,735,658	1,732,520
Total Liabilities	2,598,968	2,606,946
Starwood Property Trust, Inc. Stockholders' Equity:
Common stock	2,943	2,921
Additional paid-in capital	3,823,011	3,744,878
Treasury stock	(138,022)	(138,022)
Retained earnings (accumulated deficit)	(6,035,338)	(5,820,453)
Total Starwood Property Trust, Inc. Stockholders' Equity	(2,347,406)	(2,210,676)
Total Equity	(2,347,406)	(2,210,676)
Total Liabilities and Equity	251,562	396,270
LNR VIEs
Assets:
Cash and cash equivalents	784	772
Investment securities	(1,432,632)	(1,425,570)
Intangible assets	(42,918)	(41,376)
Investment in unconsolidated entities	(15,882)	(16,112)
Accrued interest receivable	(132)	(134)
Other assets	(16)	(7)
Total Assets	60,876,314	62,755,901
Liabilities:
Accounts payable, accrued expenses and other liabilities	91	75
Secured financing agreements, net	(21,843)	(22,000)
Total Liabilities	60,874,957	62,754,446
Starwood Property Trust, Inc. Stockholders' Equity:
Non-controlling interests in consolidated subsidiaries	1,357	1,455
Total Equity	1,357	1,455
Total Liabilities and Equity	60,876,314	62,755,901
Primary beneficiary
Assets:
Total Assets	62,367,110	64,238,328
Liabilities:
Total Liabilities	60,896,709	62,776,371
Primary beneficiary | LNR VIEs
Assets:
Total Assets	62,367,110	64,238,328
Liabilities:
Total Liabilities	$ 60,896,709	$ 62,776,371