Reportable Operating Segments - Selected Business Segment Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Selected business segment financial information
Net interest income (expense)	$ 138,683	$ 145,089
Provision for credit losses	(41,200)	(5,680)
Net interest income after provision for loan and lease losses	97,483	139,409
Noninterest income	49,228	47,072
Noninterest expense	(96,466)	(92,623)
Income before provision for income taxes	50,245	93,858
(Provision) benefit for income taxes	(11,380)	(23,934)
Net income (loss)	38,865	69,924
Assets	20,755,891		$ 20,166,734
Retail Banking
Selected business segment financial information
Net interest income (expense)	89,883	107,227
Provision for credit losses	(20,065)	(2,572)
Net interest income after provision for loan and lease losses	69,818	104,655
Noninterest income	26,376	23,869
Noninterest expense	(61,644)	(57,167)
Income before provision for income taxes	34,550	71,357
(Provision) benefit for income taxes	(7,523)	(18,047)
Net income (loss)	27,027	53,310
Commercial Banking
Selected business segment financial information
Net interest income (expense)	34,414	34,656
Provision for credit losses	(20,784)	(3,108)
Net interest income after provision for loan and lease losses	13,630	31,548
Noninterest income	17,796	18,388
Noninterest expense	(21,505)	(19,485)
Income before provision for income taxes	9,921	30,451
(Provision) benefit for income taxes	(2,645)	(7,921)
Net income (loss)	7,276	22,530
Treasury and Other
Selected business segment financial information
Net interest income (expense)	14,386	3,206
Provision for credit losses	(351)
Net interest income after provision for loan and lease losses	14,035	3,206
Noninterest income	5,056	4,815
Noninterest expense	(13,317)	(15,971)
Income before provision for income taxes	5,774	(7,950)
(Provision) benefit for income taxes	(1,212)	2,034
Net income (loss)	$ 4,562	$ (5,916)