Summary of Significant Accounting and Reporting Policies - Basis of Presentation, Ownership (Details)	9 Months Ended
	Sep. 30, 2017 item
Basis of Presentation
Number of primary business units	3
PPC
Basis of Presentation
Ownership percentage of subsidiary owned by the reporting entity	100.00%
PlainsCapital
Basis of Presentation
Ownership percentage of subsidiary owned by subsidiary of the reporting entity	100.00%
Plains Capital Equity LLC
Basis of Presentation
Ownership percentage of subsidiary owned by subsidiary of the reporting entity	100.00%
PrimeLending
Basis of Presentation
Ownership percentage of subsidiary owned by subsidiary of the reporting entity	100.00%
Ventures Management
Basis of Presentation
Ownership percentage of subsidiary owned by subsidiary of the reporting entity	100.00%
PCC Statutory Trusts
Basis of Presentation
Ownership percentage of subsidiary owned by subsidiary of the reporting entity	100.00%
Securities Holdings
Basis of Presentation
Ownership percentage of subsidiary owned by the reporting entity	100.00%
NLC
Basis of Presentation
Ownership percentage of subsidiary owned by the reporting entity	100.00%