Changes in Fair Value of Loans Held for Sale (Detail) - USD ($) $ in Thousands		3 Months Ended			9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	[2]	Sep. 30, 2017	Sep. 30, 2016	[2]
Fair Value, Option, Quantitative Disclosures [Line Items]
Mortgage Banking Income	[1]	$ (9,279)	$ (9,937)		$ (19,033)	$ (74,216)
Loans held for sale
Fair Value, Option, Quantitative Disclosures [Line Items]
Mortgage Banking Income	[1]	464	(1,020)		1,059	2,782
Mortgage servicing rights
Fair Value, Option, Quantitative Disclosures [Line Items]
Mortgage Banking Income	[1]	$ (9,743)	$ (8,917)		$ (20,092)	$ (76,998)

[1] Does not include the effect of economic hedging activities, which is included in "Other non-interest income."

[2] The presentation of the amounts for the three and nine months ended September 30, 2016 has been modified to conform to the presentation for the three and nine months ended September 30, 2017.