Reportable Operating Segments - Selected Business Segment Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Selected business segment financial information
Net interest income (expense)	$ 143,081	$ 141,258	$ 433,783	$ 422,333
Provision for loan and lease losses		(4,460)	(9,550)	(16,430)
Net interest income after provision for loan and lease losses	143,081	136,798	424,233	405,903
Noninterest income	49,980	47,405	145,825	145,902
Noninterest expense	(93,466)	(93,147)	(279,379)	(275,599)
Income before provision for income taxes	99,595	91,056	290,679	276,206
(Provision) benefit for income taxes	(25,396)	(23,668)	(74,123)	(71,807)
Net income	74,199	67,388	216,556	204,399
Retail Banking
Selected business segment financial information
Net interest income (expense)	111,529	111,804	339,559	332,731
Provision for loan and lease losses		(1,760)	(4,324)	(6,484)
Net interest income after provision for loan and lease losses	111,529	110,044	335,235	326,247
Noninterest income	24,249	22,676	72,107	67,566
Noninterest expense	(57,280)	(58,069)	(173,938)	(170,114)
Income before provision for income taxes	78,498	74,651	233,404	223,699
(Provision) benefit for income taxes	(19,941)	(19,450)	(59,338)	(58,291)
Net income	58,557	55,201	174,066	165,408
Commercial Banking
Selected business segment financial information
Net interest income (expense)	29,359	29,639	85,920	86,320
Provision for loan and lease losses		(2,700)	(5,226)	(9,946)
Net interest income after provision for loan and lease losses	29,359	26,939	80,694	76,374
Noninterest income	17,146	17,801	53,645	59,264
Noninterest expense	(20,073)	(19,731)	(59,299)	(60,575)
Income before provision for income taxes	26,432	25,009	75,040	75,063
(Provision) benefit for income taxes	(6,781)	(6,435)	(19,278)	(19,329)
Net income	19,651	18,574	55,762	55,734
Treasury and Other
Selected business segment financial information
Net interest income (expense)	2,193	(185)	8,304	3,282
Net interest income after provision for loan and lease losses	2,193	(185)	8,304	3,282
Noninterest income	8,585	6,928	20,073	19,072
Noninterest expense	(16,113)	(15,347)	(46,142)	(44,910)
Income before provision for income taxes	(5,335)	(8,604)	(17,765)	(22,556)
(Provision) benefit for income taxes	1,326	2,217	4,493	5,813
Net income	$ (4,009)	$ (6,387)	$ (13,272)	$ (16,743)