Segment Data - Balance sheets (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015
Assets:
Cash and cash equivalents	$ 413,845		$ 615,522
Restricted cash	54,591		35,233
Loans held-for-investment, net	6,382,371		5,847,995
Loans held-for-sale	608,624		63,279
Loans transferred as secured borrowings	74,339		35,000
Investment securities	701,818		807,618
Properties, net	2,521,342		1,944,720
Intangible assets	181,865		219,248
Investment in unconsolidated entities	243,450		204,605
Goodwill	140,437		140,437
Derivative assets	38,293		89,361
Accrued interest receivable	35,047		28,224
Other assets	112,265		101,763
VIE assets, at fair value	51,197,981		67,123,261
Total Assets	62,706,268		77,256,266
Liabilities:
Accounts payable, accrued expenses and other liabilities	203,782		198,134
Related-party payable	29,989		37,818
Dividends payable	125,674		125,075
Derivative liabilities	22,890		3,904
Secured financing agreements, net	5,514,695		4,154,126
Unsecured senior notes, net	2,044,523		2,011,544
Secured borrowings on transferred loans, net	74,200		35,000
VIE liabilities, at fair value	50,150,781		66,130,592
Total Liabilities	58,166,534		72,696,193
Starwood Property Trust, Inc. Stockholders' Equity:
Common stock	2,654		2,639
Additional paid-in capital	4,705,044		4,691,180
Treasury stock	(92,104)		(92,104)
Accumulated other comprehensive income (loss)	65,271	$ 55,981	36,138	$ 40,248	$ 32,627	$ 29,729
Retained earnings (accumulated deficit)	(184,073)		(115,579)
Total Starwood Property Trust, Inc. Stockholders' Equity	4,496,792		4,522,274
Non-controlling interests in consolidated subsidiaries	42,942		37,799
Total Equity	4,539,734		4,560,073	$ 4,105,382		$ 4,170,943
Total Liabilities and Equity	62,706,268		77,256,266
Investment and Servicing Segment
Assets:
Goodwill	0
Operating Segments and Corporate
Assets:
Cash and cash equivalents	408,684		614,374
Restricted cash	54,591		35,233
Loans held-for-investment, net	6,382,371		5,847,995
Loans held-for-sale	608,624		63,279
Loans transferred as secured borrowings	74,339		35,000
Investment securities	1,704,611		1,766,642
Properties, net	2,521,342		1,944,720
Intangible assets	208,447		253,486
Investment in unconsolidated entities	264,210		212,227
Goodwill	140,437		140,437
Derivative assets	38,293		89,361
Accrued interest receivable	35,047		28,224
Other assets	115,071		104,408
Total Assets	12,556,067		11,135,386
Liabilities:
Accounts payable, accrued expenses and other liabilities	202,684		197,248
Related-party payable	29,989		37,818
Dividends payable	125,674		125,075
Derivative liabilities	22,890		3,904
Secured financing agreements, net	5,538,395		4,177,826
Unsecured senior notes, net	2,044,523		2,011,544
Secured borrowings on transferred loans, net	74,200		35,000
Total Liabilities	8,038,355		6,588,415
Starwood Property Trust, Inc. Stockholders' Equity:
Common stock	2,654		2,639
Additional paid-in capital	4,705,044		4,691,180
Treasury stock	(92,104)		(92,104)
Accumulated other comprehensive income (loss)	65,271		36,138
Retained earnings (accumulated deficit)	(184,073)		(115,579)
Total Starwood Property Trust, Inc. Stockholders' Equity	4,496,792		4,522,274
Non-controlling interests in consolidated subsidiaries	20,920		24,697
Total Equity	4,517,712		4,546,971
Total Liabilities and Equity	12,556,067		11,135,386
Operating segment | Lending Segment
Assets:
Cash and cash equivalents	43,513		7,085
Restricted cash	22,527		17,885
Loans held-for-investment, net	6,378,468		5,827,553
Loans held-for-sale	418,618
Loans transferred as secured borrowings	74,339		35,000
Investment securities	677,977		776,072
Investment in unconsolidated entities	36,831		30,874
Derivative assets	13,513		45,282
Accrued interest receivable	34,569		25,831
Other assets	10,286		13,470
Total Assets	7,710,641		6,779,052
Liabilities:
Accounts payable, accrued expenses and other liabilities	27,821		20,769
Derivative liabilities	14,105		3,388
Secured financing agreements, net	3,223,863		2,258,462
Secured borrowings on transferred loans, net	74,200		35,000
Total Liabilities	3,339,989		2,317,619
Starwood Property Trust, Inc. Stockholders' Equity:
Additional paid-in capital	1,808,624		2,218,671
Accumulated other comprehensive income (loss)	55,687		44,903
Retained earnings (accumulated deficit)	2,495,536		2,186,727
Total Starwood Property Trust, Inc. Stockholders' Equity	4,359,847		4,450,301
Non-controlling interests in consolidated subsidiaries	10,805		11,132
Total Equity	4,370,652		4,461,433
Total Liabilities and Equity	7,710,641		6,779,052
Operating segment | Investment and Servicing Segment
Assets:
Cash and cash equivalents	58,584		7,701
Restricted cash	11,875		9,146
Loans held-for-investment, net	3,903
Loans held-for-sale	190,006
Investment securities	1,026,634
Properties, net	286,696		1,667,108
Intangible assets	91,591		128,159
Investment in unconsolidated entities	117,772		124,977
Goodwill	140,437
Derivative assets	2,300		42,893
Accrued interest receivable	478
Other assets	61,787		29,569
Total Assets	1,992,063		2,009,553
Liabilities:
Accounts payable, accrued expenses and other liabilities	78,398		81,873
Related-party payable	43
Derivative liabilities	1
Secured financing agreements, net	516,933		1,196,830
Total Liabilities	595,375		1,278,703
Starwood Property Trust, Inc. Stockholders' Equity:
Additional paid-in capital	747,298		696,049
Accumulated other comprehensive income (loss)	(84)		(8,328)
Retained earnings (accumulated deficit)	639,359		43,129
Total Starwood Property Trust, Inc. Stockholders' Equity	1,386,573		730,850
Non-controlling interests in consolidated subsidiaries	10,115
Total Equity	1,396,688		730,850
Total Liabilities and Equity	1,992,063		2,009,553
Operating segment | Property Segment
Assets:
Cash and cash equivalents	8,581		38,798
Restricted cash	20,189		8,202
Loans held-for-investment, net			20,442
Loans held-for-sale			63,279
Investment securities			990,570
Properties, net	2,234,646		277,612
Intangible assets	116,856		125,327
Investment in unconsolidated entities	109,607		56,376
Goodwill			140,437
Derivative assets	22,480		1,186
Accrued interest receivable			2,393
Other assets	40,705		59,503
Total Assets	2,553,064		1,784,125
Liabilities:
Accounts payable, accrued expenses and other liabilities	71,726		68,603
Related-party payable			440
Derivative liabilities	8,784		516
Secured financing agreements, net	1,501,006		426,683
Total Liabilities	1,581,516		496,242
Starwood Property Trust, Inc. Stockholders' Equity:
Additional paid-in capital	981,129		883,761
Accumulated other comprehensive income (loss)	9,668		(437)
Retained earnings (accumulated deficit)	(19,249)		390,994
Total Starwood Property Trust, Inc. Stockholders' Equity	971,548		1,274,318
Non-controlling interests in consolidated subsidiaries			13,565
Total Equity	971,548		1,287,883
Total Liabilities and Equity	2,553,064		1,784,125
Corporate
Assets:
Cash and cash equivalents	298,006		560,790
Other assets	2,293		1,866
Total Assets	300,299		562,656
Liabilities:
Accounts payable, accrued expenses and other liabilities	24,739		26,003
Related-party payable	29,946		37,378
Dividends payable	125,674		125,075
Secured financing agreements, net	296,593		295,851
Unsecured senior notes, net	2,044,523		2,011,544
Total Liabilities	2,521,475		2,495,851
Starwood Property Trust, Inc. Stockholders' Equity:
Common stock	2,654		2,639
Additional paid-in capital	1,167,993		892,699
Treasury stock	(92,104)		(92,104)
Retained earnings (accumulated deficit)	(3,299,719)		(2,736,429)
Total Starwood Property Trust, Inc. Stockholders' Equity	(2,221,176)		(1,933,195)
Total Equity	(2,221,176)		(1,933,195)
Total Liabilities and Equity	300,299		562,656
Investment and Servicing VIEs
Assets:
Cash and cash equivalents	5,161		1,148
Investment securities	(1,002,793)		(959,024)
Intangible assets	(26,582)		(34,238)
Investment in unconsolidated entities	(20,760)		(7,622)
Other assets	(2,806)		(2,645)
VIE assets, at fair value	51,197,981		67,123,261
Total Assets	50,150,201		66,120,880
Liabilities:
Accounts payable, accrued expenses and other liabilities	1,098		886
Secured financing agreements, net	(23,700)		(23,700)
VIE liabilities, at fair value	50,150,781		66,130,592
Total Liabilities	50,128,179		66,107,778
Starwood Property Trust, Inc. Stockholders' Equity:
Non-controlling interests in consolidated subsidiaries	22,022		13,102
Total Equity	22,022		13,102
Total Liabilities and Equity	$ 50,150,201		$ 66,120,880