Reportable Operating Segments - Selected Business Segment Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Selected business segment financial information
Net interest income	$ 129,158	$ 138,683
Benefit (Provision) for credit losses		(41,200)
Net interest income after provision for credit losses	129,158	97,483
Noninterest income	43,868	49,228
Noninterest expense	(96,306)	(96,466)
Income before provision for income taxes	76,720	50,245
(Provision) benefit for income taxes	(19,027)	(11,380)
Net income	57,693	38,865
Retail Banking
Selected business segment financial information
Net interest income	100,888	89,883
Benefit (Provision) for credit losses	1,470	(20,065)
Net interest income after provision for credit losses	102,358	69,818
Noninterest income	23,575	26,376
Noninterest expense	(63,794)	(61,644)
Income before provision for income taxes	62,139	34,550
(Provision) benefit for income taxes	(15,502)	(7,523)
Net income	46,637	27,027
Commercial Banking
Selected business segment financial information
Net interest income	31,832	34,414
Benefit (Provision) for credit losses	2,030	(20,784)
Net interest income after provision for credit losses	33,862	13,630
Noninterest income	16,041	17,796
Noninterest expense	(21,573)	(21,505)
Income before provision for income taxes	28,330	9,921
(Provision) benefit for income taxes	(6,968)	(2,645)
Net income	21,362	7,276
Treasury and Other
Selected business segment financial information
Net interest income	(3,562)	14,386
Benefit (Provision) for credit losses	(3,500)	(351)
Net interest income after provision for credit losses	(7,062)	14,035
Noninterest income	4,252	5,056
Noninterest expense	(10,939)	(13,317)
Income before provision for income taxes	(13,749)	5,774
(Provision) benefit for income taxes	3,443	(1,212)
Net income	$ (10,306)	$ 4,562