Loans - Changes in Accretable Yield for PCI Loans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance, beginning of period	$ 294,514	$ 415,179
Accretion	(89,770)	(107,482)
Net increase (decrease) in expected cash flows	77,265	(9,989)
Other, net	0	(3,194)
Balance, end of period	$ 282,009	$ 294,514