Note Other comprehensive income (loss) (Reclassification out of accumulated other comprehensive income (loss)) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Personnel costs	$ (125,607)	$ (127,091)
Other operating income	19,128	15,545
Net (loss) gain and valuation adjustments on investment securities	162	0
Mortgage banking activities	11,369	10,551
Income tax (benefit) expense	(33,006)	(32,265)
Net Income	92,945	84,999
Reclassification out of accumulated other comprehensive income
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net Income	(3,233)	(3,709)
Reclassification out of accumulated other comprehensive income | Adjustment of pension and postretirement benefit plan
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Total before tax	(4,657)	(4,536)
Income tax (benefit) expense	1,816	1,770
Net Income	(2,841)	(2,766)
Reclassification out of accumulated other comprehensive income | Adjustment of pension and postretirement benefit plan | Amortization of net losses
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Personnel costs	(5,607)	(5,486)
Reclassification out of accumulated other comprehensive income | Adjustment of pension and postretirement benefit plan | Amortization of prior service credit
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Personnel costs	950	950
Reclassification out of accumulated other comprehensive income | Unrealized holding (losses) gain on investments | Realized gain (loss) on sale of securities
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net (loss) gain and valuation adjustments on investment securities	162	0
Total before tax	162	0
Income tax (benefit) expense	(32)	0
Net Income	130	0
Reclassification out of accumulated other comprehensive income | Unrealized net (losses) gains on cash flow hedges | Forward contracts
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Mortgage banking activities	(855)	(1,545)
Total before tax	(855)	(1,545)
Income tax (benefit) expense	333	602
Net Income	$ (522)	$ (943)