Note FDIC loss share asset (Fair value and the undiscounted amount of the true-up payment obligation) (Detail) - FDIC - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Business Acquisition, Contingent Consideration [Line Items]
Carrying amount (fair value)	$ 170,970	$ 164,858
Undiscounted amount	$ 189,449	$ 188,958