Cover Page - USD ($)	12 Months Ended
	Dec. 31, 2021	Mar. 04, 2022	Jun. 30, 2021
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2021
Document Transition Report	false
Entity File Number	001-35543
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	27-0298092
Entity Registrant Name	Western Asset Mortgage Capital Corporation
Entity Address, Address Line One	47 W 200 S
Entity Address, City or Town	Salt Lake City
Entity Address, State or Province	UT
Entity Address, Postal Zip Code	84101
City Area Code	(626)
Local Phone Number	844-9400
Title of 12(b) Security	Common Stock, $0.01 par value
Trading Symbol	WMC
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Central Index Key	0001465885
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 187,567,608
Entity Common Stock, Shares Outstanding (in shares)		60,380,105
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Amendment Flag	false