Other comprehensive income (loss) - Reclassification out of accumulated other comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Reclassification out of accumulated other comprehensive loss
Income tax (benefit) expense	$ (24,628)	$ (40,330)	$ (27,725)	$ (90,553)
Net income	127,628	171,106	161,930	339,031
Reclassification out of accumulated other comprehensive income
Reclassification out of accumulated other comprehensive loss
Net income	(4,802)	(4,229)	(8,994)	(8,546)
Reclassification out of accumulated other comprehensive income | Adjustment of pension and postretirement benefit plan
Reclassification out of accumulated other comprehensive loss
Income (loss) before tax	(5,362)	(5,876)	(10,724)	(11,752)
Income tax (benefit) expense	2,011	2,204	4,022	4,407
Net income	(3,351)	(3,672)	(6,702)	(7,345)
Reclassification out of accumulated other comprehensive income | Amortization of net Loss | Personnel costs
Reclassification out of accumulated other comprehensive loss
Income (loss) before tax	(5,362)	(5,876)	(10,724)	(11,752)
Reclassification out of accumulated other comprehensive income | Unrealized net (losses) gains on cash flow hedges
Reclassification out of accumulated other comprehensive loss
Income (loss) before tax	(2,187)	(891)	(3,514)	(1,921)
Income tax (benefit) expense	736	334	1,222	720
Net income	(1,451)	(557)	(2,292)	(1,201)
Reclassification out of accumulated other comprehensive income | Unrealized net (losses) gains on cash flow hedges | Forward contracts | Mortgage banking activities
Reclassification out of accumulated other comprehensive loss
Income (loss) before tax	(1,963)	(891)	(3,259)	(1,921)
Reclassification out of accumulated other comprehensive income | Unrealized net (losses) gains on cash flow hedges | Interest rate swap
Reclassification out of accumulated other comprehensive loss
Other Operating Income	$ (224)	$ 0	$ (255)	$ 0