Changes in Fair Value of Loans Held for Sale (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Option, Quantitative Disclosures [Line Items]
Mortgage Banking Income	[1]	$ (224)	$ (19,177)	$ (33,069)
Loans held for sale
Fair Value, Option, Quantitative Disclosures [Line Items]
Mortgage Banking Income	[1]		899	(5,616)
Mortgage servicing rights
Fair Value, Option, Quantitative Disclosures [Line Items]
Mortgage Banking Income	[1]	$ (224)	$ (20,076)	$ (27,453)

[1] Included in “Non-interest income.”