Accumulated Other Comprehensive Income (Loss) - Reclassifications out of AOCI - (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Reclassifications out of accumulated other comprehensive income, net of tax
Interest expense	$ (15,271)	$ (4,092)	$ (36,516)	$ (11,464)
Other noninterest income	2,659	1,367	7,738	4,532
Other-than-temporary impairment losses		(753)		(753)
Provision for income taxes	(9,823)	(17,677)	(32,752)	(40,710)
Net income	47,082	35,046	129,867	85,133
Amount Reclassified from Accumulated Other Comprehensive Loss
Reclassifications out of accumulated other comprehensive income, net of tax
Net income	187	(640)	1,055	(370)
Gains and Losses on Cash Flow Hedges | Amount Reclassified from Accumulated Other Comprehensive Loss
Reclassifications out of accumulated other comprehensive income, net of tax
Securities (gains) losses, net	11	(1,278)	652	(1,388)
Provision for income taxes	(2)	487	(144)	529
Net income	9	(791)	508	(859)
Gains and Losses on Cash Flow Hedges | Amount Reclassified from Accumulated Other Comprehensive Loss | Interest rate contracts
Reclassifications out of accumulated other comprehensive income, net of tax
Interest expense	35	57	121	226
Provision for income taxes	(8)	(22)	(27)	(86)
Net income	27	35	94	140
Noncredit Other-Than-Temporary Impairment Losses | Amount Reclassified from Accumulated Other Comprehensive Loss
Reclassifications out of accumulated other comprehensive income, net of tax
Other-than-temporary impairment losses		753		753
Provision for income taxes		(287)		(287)
Net income		466		466
Benefit Plans | Amount Reclassified from Accumulated Other Comprehensive Loss
Reclassifications out of accumulated other comprehensive income, net of tax
Salaries and employee benefits	194	188	581	564
Provision for income taxes	(43)	(72)	(128)	(215)
Net income	$ 151	$ 116	$ 453	$ 349