Segment and Geographic Data - Balance sheets (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Assets:
Cash and cash equivalents	$ 334,288		$ 239,824
Restricted cash	181,910		248,041
Loans held-for-investment, net	8,764,216		8,532,356
Loans held-for-sale	1,586,899		1,187,552
Loans transferred as secured borrowings			74,346
Investment securities	849,572		906,468
Properties, net	2,771,960		2,784,890
Intangible assets	129,477		145,033
Investment in unconsolidated entities	119,876		171,765
Goodwill	259,846		259,846
Derivative assets	53,676		52,691
Accrued interest receivable	61,380		60,355
Other assets	166,655		152,922
VIE assets, at fair value	57,667,606		53,446,364
Total Assets	72,947,361		68,262,453
Liabilities:
Accounts payable, accrued expenses and other liabilities	221,434		217,663
Related-party payable	21,144		44,043
Dividends payable	136,424		133,466
Derivative liabilities	8,891		15,415
Secured financing agreements, net	9,284,887		8,683,565
Unsecured senior notes, net	1,924,711		1,998,831
Secured borrowings on transferred loans, net			74,239
VIE liabilities, at fair value	56,446,619		52,195,042
Total Liabilities	68,044,110		63,362,264
Starwood Property Trust, Inc. Stockholders' Equity:
Common stock	2,864		2,808
Additional paid-in capital	5,103,771		4,995,156
Treasury stock	(104,194)		(104,194)
Accumulated other comprehensive income (loss)	57,124	$ 55,798	58,660	$ 68,134	$ 75,310	$ 69,924
Retained earnings (accumulated deficit)	(421,858)		(348,998)
Total Starwood Property Trust, Inc. Stockholders' Equity	4,637,707		4,603,432
Non-controlling interests in consolidated subsidiaries	265,544		296,757
Total Equity	4,903,251	$ 4,916,967	4,900,189	$ 4,699,691	$ 4,704,687	$ 4,579,201
Total Liabilities and Equity	72,947,361		68,262,453
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	333,189		237,270
Restricted cash	181,910		248,041
Loans held-for-investment, net	8,764,216		8,532,356
Loans held-for-sale	1,586,899		1,187,552
Loans transferred as secured borrowings			74,346
Investment securities	2,028,494		2,110,508
Properties, net	2,771,960		2,784,890
Intangible assets	153,560		169,108
Investment in unconsolidated entities	142,473		193,765
Goodwill	259,846		259,846
Derivative assets	53,676		52,691
Accrued interest receivable	62,149		60,996
Other assets	166,645		152,948
Total Assets	16,505,017		16,064,317
Liabilities:
Accounts payable, accrued expenses and other liabilities	221,358		217,521
Related-party payable	21,144		44,043
Dividends payable	136,424		133,466
Derivative liabilities	8,891		15,415
Secured financing agreements, net	9,298,837		8,697,515
Unsecured senior notes, net	1,924,711		1,998,831
Secured borrowings on transferred loans, net			74,239
Total Liabilities	11,611,365		11,181,030
Starwood Property Trust, Inc. Stockholders' Equity:
Common stock	2,864		2,808
Additional paid-in capital	5,103,771		4,995,156
Treasury stock	(104,194)		(104,194)
Accumulated other comprehensive income (loss)	57,124		58,660
Retained earnings (accumulated deficit)	(421,858)		(348,998)
Total Starwood Property Trust, Inc. Stockholders' Equity	4,637,707		4,603,432
Non-controlling interests in consolidated subsidiaries	255,945		279,855
Total Equity	4,893,652		4,883,287
Total Liabilities and Equity	16,505,017		16,064,317
Operating segment | Commercial and Residential Lending Segment
Assets:
Cash and cash equivalents	21,709		14,385
Restricted cash	34,070		28,324
Loans held-for-investment, net	7,406,274		7,072,220
Loans held-for-sale	1,156,778		670,155
Loans transferred as secured borrowings			74,346
Investment securities	957,783		1,050,920
Properties, net	27,150
Investment in unconsolidated entities	36,336		35,274
Derivative assets	21,604		18,174
Accrued interest receivable	42,644		39,862
Other assets	15,048		13,958
Total Assets	9,719,396		9,017,618
Liabilities:
Accounts payable, accrued expenses and other liabilities	33,625		26,508
Derivative liabilities	5,966		1,290
Secured financing agreements, net	5,177,123		4,405,599
Secured borrowings on transferred loans, net			74,239
Total Liabilities	5,216,714		4,507,636
Starwood Property Trust, Inc. Stockholders' Equity:
Additional paid-in capital	1,203,757		1,430,503
Accumulated other comprehensive income (loss)	53,050		53,516
Retained earnings (accumulated deficit)	3,245,875		3,015,676
Total Starwood Property Trust, Inc. Stockholders' Equity	4,502,682		4,499,695
Non-controlling interests in consolidated subsidiaries			10,287
Total Equity	4,502,682		4,509,982
Total Liabilities and Equity	9,719,396		9,017,618
Operating segment | Infrastructure Lending Segment
Assets:
Cash and cash equivalents	126		13
Restricted cash	111,076		175,659
Loans held-for-investment, net	1,356,511		1,456,779
Loans held-for-sale	214,501		469,775
Investment securities	55,332		60,768
Goodwill	119,409		119,409
Derivative assets	357		1,066
Accrued interest receivable	5,512		6,982
Other assets	4,645		20,472
Total Assets	1,867,469		2,310,923
Liabilities:
Accounts payable, accrued expenses and other liabilities	4,099		26,476
Derivative liabilities	435		477
Secured financing agreements, net	1,237,526		1,524,551
Total Liabilities	1,242,060		1,551,504
Starwood Property Trust, Inc. Stockholders' Equity:
Additional paid-in capital	624,494		761,992
Retained earnings (accumulated deficit)	915		(2,573)
Total Starwood Property Trust, Inc. Stockholders' Equity	625,409		759,419
Total Equity	625,409		759,419
Total Liabilities and Equity	1,867,469		2,310,923
Operating segment | Property Segment
Assets:
Cash and cash equivalents	30,493		27,408
Restricted cash	21,598		25,144
Properties, net	2,476,175		2,512,847
Intangible assets	80,840		90,889
Investment in unconsolidated entities	71,601		114,362
Derivative assets	17,857		32,733
Accrued interest receivable	350		359
Other assets	71,166		67,098
Total Assets	2,770,080		2,870,840
Liabilities:
Accounts payable, accrued expenses and other liabilities	61,947		67,415
Derivative liabilities			37
Secured financing agreements, net	1,882,956		1,884,187
Total Liabilities	1,944,903		1,951,639
Starwood Property Trust, Inc. Stockholders' Equity:
Additional paid-in capital	625,962		645,561
Accumulated other comprehensive income (loss)	4,139		5,208
Retained earnings (accumulated deficit)	(43,051)		13,570
Total Starwood Property Trust, Inc. Stockholders' Equity	587,050		664,339
Non-controlling interests in consolidated subsidiaries	238,127		254,862
Total Equity	825,177		919,201
Total Liabilities and Equity	2,770,080		2,870,840
Operating segment | Investing and Servicing Segment
Assets:
Cash and cash equivalents	27,082		31,449
Restricted cash	15,166		11,679
Loans held-for-investment, net	1,431		3,357
Loans held-for-sale	215,620		47,622
Investment securities	1,015,379		998,820
Properties, net	268,635		272,043
Intangible assets	72,720		78,219
Investment in unconsolidated entities	34,536		44,129
Goodwill	140,437		140,437
Derivative assets	44		718
Accrued interest receivable	366		616
Other assets	66,564		49,363
Total Assets	1,857,980		1,678,452
Liabilities:
Accounts payable, accrued expenses and other liabilities	68,021		75,655
Related-party payable	11		53
Derivative liabilities	2,490		1,423
Secured financing agreements, net	702,781		585,258
Total Liabilities	773,303		662,389
Starwood Property Trust, Inc. Stockholders' Equity:
Additional paid-in capital	49,768		87,779
Accumulated other comprehensive income (loss)	(65)		(64)
Retained earnings (accumulated deficit)	1,017,156		913,642
Total Starwood Property Trust, Inc. Stockholders' Equity	1,066,859		1,001,357
Non-controlling interests in consolidated subsidiaries	17,818		14,706
Total Equity	1,084,677		1,016,063
Total Liabilities and Equity	1,857,980		1,678,452
Corporate
Assets:
Cash and cash equivalents	253,779		164,015
Restricted cash			7,235
Derivative assets	13,814
Accrued interest receivable	13,277		13,177
Other assets	9,222		2,057
Total Assets	290,092		186,484
Liabilities:
Accounts payable, accrued expenses and other liabilities	53,666		21,467
Related-party payable	21,133		43,990
Dividends payable	136,424		133,466
Derivative liabilities			12,188
Secured financing agreements, net	298,451		297,920
Unsecured senior notes, net	1,924,711		1,998,831
Total Liabilities	2,434,385		2,507,862
Starwood Property Trust, Inc. Stockholders' Equity:
Common stock	2,864		2,808
Additional paid-in capital	2,599,790		2,069,321
Treasury stock	(104,194)		(104,194)
Retained earnings (accumulated deficit)	(4,642,753)		(4,289,313)
Total Starwood Property Trust, Inc. Stockholders' Equity	(2,144,293)		(2,321,378)
Total Equity	(2,144,293)		(2,321,378)
Total Liabilities and Equity	290,092		186,484
LNR VIEs
Assets:
Cash and cash equivalents	1,099		2,554
Investment securities	(1,178,922)		(1,204,040)
Intangible assets	(24,083)		(24,075)
Investment in unconsolidated entities	(22,597)		(22,000)
Accrued interest receivable	(769)		(641)
Other assets	10		(26)
VIE assets, at fair value	57,667,606		53,446,364
Total Assets	56,442,344		52,198,136
Liabilities:
Accounts payable, accrued expenses and other liabilities	76		142
Secured financing agreements, net	(13,950)		(13,950)
VIE liabilities, at fair value	56,446,619		52,195,042
Total Liabilities	56,432,745		52,181,234
Starwood Property Trust, Inc. Stockholders' Equity:
Non-controlling interests in consolidated subsidiaries	9,599		16,902
Total Equity	9,599		16,902
Total Liabilities and Equity	$ 56,442,344		$ 52,198,136