Business Segments (Operating Results and Other Key Financial Measures) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Segment Reporting Information
Net interest income before provision for credit losses	$ 362,707	$ 362,461
Provision for credit losses	73,870	22,579
Noninterest Income	54,049	42,131
Noninterest expense	178,876	186,922
Segment income (loss) before income taxes	164,010	195,091
Segment net income	144,824	164,024
Segment assets	45,948,545	42,091,433	$ 44,196,096
Consumer and Business Banking
Segment Reporting Information
Net interest income before provision for credit losses	152,591	185,059
Provision for credit losses	7,788	3,013
Noninterest Income	16,402	13,772
Noninterest expense	86,964	87,906
Segment income (loss) before income taxes	74,241	107,912
Segment net income	53,195	77,146
Segment assets	11,894,691	10,902,961
Commercial Banking
Segment Reporting Information
Net interest income before provision for credit losses	183,501	152,708
Provision for credit losses	66,082	19,566
Noninterest Income	32,456	24,544
Noninterest expense	70,126	70,544
Segment income (loss) before income taxes	79,749	87,142
Segment net income	57,131	62,334
Segment assets	26,412,726	23,964,592
Other
Segment Reporting Information
Net interest income before provision for credit losses	26,615	24,694
Provision for credit losses	0	0
Noninterest Income	5,191	3,815
Noninterest expense	21,786	28,472
Segment income (loss) before income taxes	10,020	37
Segment net income	34,498	24,544
Segment assets	$ 7,641,128	$ 7,223,880