Covered Assets and Indemnification Asset - Indemnification Asset (Details) - PlainsCapital - FNB - Covered - USD ($) $ in Millions	Sep. 13, 2013	Sep. 30, 2017
Loans
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	$ 240.4
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	$ 365.7
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	$ 0.0
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		$ 16.1
Commercial Loan
Loans
Period of loss-sharing agreements in effect	5 years
Period of loss recovery provisions in effect	8 years
Single Family Residential Loans
Loans
Period of loss-sharing agreements in effect	10 years
Period of loss recovery provisions in effect	10 years