Accumulated Other Comprehensive Income (Loss) - Reclassifications out of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Debt securities (gains) losses, net	$ (692)		$ (511)		$ (2,685)	$ (5,685)
Income tax (expense) benefit	13,960		9,761		31,590	12,700
Interest income (expense)	(149,927)		(145,671)		(298,047)	(289,442)
Salaries and employee benefits	72,640		66,556		140,757	145,729
Net income	(62,786)	$ (86,818)	(51,705)	$ (22,640)	(149,604)	(74,345)
Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income	1,802		1,661		3,430	5,966
Amount Reclassified from AOCI | Unrealized Gains and Losses on Available- for-Sale Debt Securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Debt securities (gains) losses, net	692		511		2,685	5,685
Income tax (expense) benefit	(178)		(89)		(618)	(1,263)
Net income	514		422		2,067	4,422
Amount Reclassified from AOCI | Gains and Losses on Cash Flow Hedges | Interest rate contracts
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax (expense) benefit	(431)		(410)		(468)	(516)
Interest income (expense)	1,756		1,670		1,905	2,101
Net income	1,325		1,260		1,437	1,585
Amount Reclassified from AOCI | Defined Benefit Pension Plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax (expense) benefit	12		6		24	13
Salaries and employee benefits	(49)		(27)		(98)	(54)
Net income	$ (37)		$ (21)		$ (74)	$ (41)