Note Other comprehensive income (loss) (Reclassification out of accumulated other comprehensive income (loss)) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Reclassification adjustment for (gains) losses included in net income (loss)	$ 0	$ 0
Net Income	84,999	74,826
Reclassification out of accumulated other comprehensive income
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net Income	(3,709)	(3,314)
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	(4,536)	(4,075)
Income tax (benefit) expense	1,770	1,589
Net Income	(2,766)	(2,486)
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	(5,486)	(5,025)
Reclassification out of accumulated other comprehensive income | Adjustment of pension and postretirement benefit plan | Amortization of prior service cost
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Personnel costs	950	950
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]
Total before tax	(1,545)	(1,358)
Mortgage banking activities	(1,545)	(1,358)
Income tax (benefit) expense	602	530
Net Income	$ (943)	$ (828)