Reportable Operating Segments - Selected Business Segment Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Selected business segment financial information
Net interest income (expense)	$ 139,672	$ 129,345
Provision for loan and lease losses	(5,950)	(4,500)
Net interest income after provision for loan and lease losses	133,722	124,845
Noninterest income	48,700	51,059
Noninterest expense	(90,587)	(85,991)
Income before provision for income taxes	91,835	89,913
(Provision) benefit for income taxes	(23,877)	(33,173)
Net income	67,958	56,740
Retail Banking
Selected business segment financial information
Net interest income (expense)	109,654	105,701
Provision for loan and lease losses	(2,348)	(1,663)
Net interest income after provision for loan and lease losses	107,306	104,038
Noninterest income	22,732	23,619
Noninterest expense	(56,461)	(55,240)
Income before provision for income taxes	73,577	72,417
(Provision) benefit for income taxes	(19,207)	(26,733)
Net income	54,370	45,684
Commercial Banking
Selected business segment financial information
Net interest income (expense)	27,879	27,533
Provision for loan and lease losses	(3,602)	(2,837)
Net interest income after provision for loan and lease losses	24,277	24,696
Noninterest income	20,000	18,834
Noninterest expense	(19,648)	(16,313)
Income before provision for income taxes	24,629	27,217
(Provision) benefit for income taxes	(6,328)	(10,034)
Net income	18,301	17,183
Treasury and Other
Selected business segment financial information
Net interest income (expense)	2,139	(3,889)
Net interest income after provision for loan and lease losses	2,139	(3,889)
Noninterest income	5,968	8,606
Noninterest expense	(14,478)	(14,438)
Income before provision for income taxes	(6,371)	(9,721)
(Provision) benefit for income taxes	1,658	3,594
Net income	$ (4,713)	$ (6,127)