Changes in Fair Value of MSRs (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Mortgage servicing rights
Fair Value, Option, Quantitative Disclosures [Line Items]
Mortgage Banking Income	[1]	$ (70)	$ (30,988)	$ (224)	$ (68,081)

[1] Included in "Non-interest income."