Business Segments (Operating Results and Other Key Financial Measures) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Segment Reporting Information
Net interest income before (reversal of) provision for credit losses	$ 353,695	$ 362,707
Provision for (reversal of) credit losses	0	73,870
Noninterest income	72,866	55,506
Noninterest expense	191,077	180,333
Segment income (loss) before income taxes	235,484	164,010
Segment net income	204,994	144,824
Segment assets	56,874,146	45,948,545	$ 52,156,913
Consumer and Business Banking
Segment Reporting Information
Net interest income before (reversal of) provision for credit losses	149,899	152,591
Provision for (reversal of) credit losses	(4,249)	7,788
Noninterest income	20,828	16,402
Noninterest expense	89,286	86,964
Segment income (loss) before income taxes	85,690	74,241
Segment net income	61,378	53,195
Segment assets	14,147,094	11,894,691
Commercial Banking
Segment Reporting Information
Net interest income before (reversal of) provision for credit losses	177,092	183,501
Provision for (reversal of) credit losses	4,249	66,082
Noninterest income	50,010	32,456
Noninterest expense	69,257	70,126
Segment income (loss) before income taxes	153,596	79,749
Segment net income	110,080	57,131
Segment assets	27,222,272	26,412,726
Other
Segment Reporting Information
Net interest income before (reversal of) provision for credit losses	26,704	26,615
Provision for (reversal of) credit losses	0	0
Noninterest income	2,028	6,648
Noninterest expense	32,534	23,243
Segment income (loss) before income taxes	(3,802)	10,020
Segment net income	33,536	34,498
Segment assets	$ 15,504,780	$ 7,641,128