Loans Held for Investment - TDRs (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($) loan	Mar. 31, 2019 loan
TDRs, Non-covered loans
Number of TDR loans granted		0
Number of TDRs granted in preceding twelve months for which payment was at least 30 days past due	0	0
AB Note | Minimum | PlainsCapital (the Bank)
TDRs, Non-covered loans
Number of loans into which a single loan may be reconfigured	2
Payment Term Extension
TDRs, Non-covered loans
Number of TDR loans granted	1
TDR at extension | $	$ 1,089
TDR modifications, in which a payment was at least 30 days past due | $	$ 1,166
Commercial | Commercial And Industrial | Payment Term Extension
TDRs, Non-covered loans
Number of TDR loans granted	1
TDR at extension | $	$ 1,089
TDR modifications, in which a payment was at least 30 days past due | $	$ 1,166