Reportable Operating Segments - Selected Business Segment Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Selected business segment financial information
Net interest income (expense)	$ 141,403	$ 131,254	$ 281,075	$ 260,599
Provision for loan and lease losses	(6,020)	(4,400)	(11,970)	(8,900)
Net interest income after provision for loan and lease losses	135,383	126,854	269,105	251,699
Noninterest income	49,797	50,558	98,497	101,617
Noninterest expense	(91,865)	(86,929)	(182,452)	(172,920)
Income before provision for income taxes	93,315	90,483	185,150	180,396
(Provision) benefit for income taxes	(24,262)	(33,588)	(48,139)	(66,761)
Net income	69,053	56,895	137,011	113,635
Retail Banking
Selected business segment financial information
Net interest income (expense)	111,273	106,912	220,927	212,613
Provision for loan and lease losses	(2,376)	(1,626)	(4,724)	(3,289)
Net interest income after provision for loan and lease losses	108,897	105,286	216,203	209,324
Noninterest income	22,158	22,381	44,890	46,000
Noninterest expense	(55,584)	(56,168)	(112,045)	(111,408)
Income before provision for income taxes	75,471	71,499	149,048	143,916
(Provision) benefit for income taxes	(19,634)	(26,485)	(38,841)	(53,218)
Net income	55,837	45,014	110,207	90,698
Commercial Banking
Selected business segment financial information
Net interest income (expense)	28,802	27,726	56,681	55,259
Provision for loan and lease losses	(3,644)	(2,774)	(7,246)	(5,611)
Net interest income after provision for loan and lease losses	25,158	24,952	49,435	49,648
Noninterest income	21,463	20,197	41,463	39,031
Noninterest expense	(21,196)	(17,034)	(40,844)	(33,347)
Income before provision for income taxes	25,425	28,115	50,054	55,332
(Provision) benefit for income taxes	(6,566)	(10,409)	(12,894)	(20,443)
Net income	18,859	17,706	37,160	34,889
Treasury and Other
Selected business segment financial information
Net interest income (expense)	1,328	(3,384)	3,467	(7,273)
Net interest income after provision for loan and lease losses	1,328	(3,384)	3,467	(7,273)
Noninterest income	6,176	7,980	12,144	16,586
Noninterest expense	(15,085)	(13,727)	(29,563)	(28,165)
Income before provision for income taxes	(7,581)	(9,131)	(13,952)	(18,852)
(Provision) benefit for income taxes	1,938	3,306	3,596	6,900
Net income	$ (5,643)	$ (5,825)	$ (10,356)	$ (11,952)