Commitments and Contingencies (Details) $ in Thousands, shares in Millions		3 Months Ended
	Sep. 13, 2013 USD ($) item	Mar. 31, 2017 USD ($) shares	Mar. 31, 2016 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Reserve for Indemnification Liability:
FDIC, collections received		$ 140,300
Representation and Warranty Claims
Roll-forward of claims activity for loans put-back to the mortgage origination segment
Balance, beginning of period		40,669	$ 57,298
Claims made		8,379	4,548
Claims resolved with no payment		(8,098)	(6,115)
Repurchases		(1,461)	(1,157)
Indemnification payments		(244)	(372)
Balance, end of period		39,245	54,202
Reserve for Indemnification Liability:
Total		40,669	57,298	$ 39,245	$ 40,669
Indemnification Agreement
Commitments and Contingencies
Provision for indemnification losses		800	900
Roll-forward of claims activity for loans put-back to the mortgage origination segment
Balance, beginning of period		18,239	16,640
Additions for new sales		847	878
Repurchases		(102)	(112)
Early payment defaults		(69)	(90)
Indemnification payments		(42)	(169)
Change in estimate		79
Balance, end of period		18,952	17,147
Reserve for Indemnification Liability:
Specific claims				1,751	1,661
Incurred but not reported claims				17,201	16,578
Total		$ 18,239	$ 16,640	18,952	$ 18,239
Shareholder Class Action Lawsuits
Commitments and Contingencies
Number of shares of SWS common stock held by purported shareholders | shares		5.2
PlainsCapital | FNB | Covered
Reserve for Indemnification Liability:
Number of loss-sharing agreements | item	2
Loans and OREO acquired	$ 1,200,000
Percentage of net losses to be absorbed by FDIC on the first $240.4 million of net losses incurred as per the loss sharing agreement	80.00%
Threshold amount of net losses incurred for 80% of net losses to be absorbed by FDIC as per the loss sharing agreement, first layer	$ 240,400
Percentage of net losses to be absorbed by FDIC in excess of $240.4 million up to and including $365.7 million of net losses incurred as per the loss sharing agreement	0.00%
Threshold amount of net losses incurred for 0% of net losses to be absorbed by FDIC as per the loss sharing agreement, second layer	$ 365,700
Percentage of net losses to be absorbed by FDIC in excess of $365.7 million of net losses incurred as per the loss sharing agreement	80.00%
Threshold limit of subsequent recoveries reimbursable to the FDIC under the loss share agreement	$ 0
Period for which payment is required to be made to the FDIC of true-up amount	10 years
Payment accrual based on the current aggregate estimate of realized losses				$ 14,900
Percentage of initial estimate of losses under loss sharing agreement		80.00%
Amount of initial estimate of losses under loss sharing agreement		$ 240,400
Covered net losses billed to the FDIC		$ 175,400
Percentage of covered net losses reimbursable under the loss-share agreements		80.00%
Amount of covered net losses reimbursable under the loss-share agreements		$ 140,300
FDIC, collections received		$ 140,300
PlainsCapital | FNB | Covered | Commercial Loan
Reserve for Indemnification Liability:
Period of loss-sharing agreements in effect	5 years
Period of loss recovery provisions in effect	8 years
PlainsCapital | FNB | Covered | Single Family Residential Loans
Reserve for Indemnification Liability:
Period of loss-sharing agreements in effect	10 years
Period of loss recovery provisions in effect	10 years