Reportable Operating Segments - Selected Business Segment Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Selected business segment financial information
Net interest income	$ 145,089	$ 139,672
Provision for loan and lease losses	(5,680)	(5,950)
Net interest income after provision for loan and lease losses	139,409	133,722
Noninterest income	47,072	48,700
Noninterest expense	(92,623)	(90,587)
Income before provision for income taxes	93,858	91,835
(Provision) benefit for income taxes	(23,934)	(23,877)
Net income (loss)	69,924	67,958
Retail Banking
Selected business segment financial information
Net interest income	113,903	109,654
Provision for loan and lease losses	(2,572)	(2,348)
Net interest income after provision for loan and lease losses	111,331	107,306
Noninterest income	24,176	22,732
Noninterest expense	(57,166)	(56,461)
Income before provision for income taxes	78,341	73,577
(Provision) benefit for income taxes	(19,927)	(19,207)
Net income (loss)	58,414	54,370
Commercial Banking
Selected business segment financial information
Net interest income	27,980	27,879
Provision for loan and lease losses	(3,108)	(3,602)
Net interest income after provision for loan and lease losses	24,872	24,277
Noninterest income	18,081	20,000
Noninterest expense	(19,485)	(19,648)
Income before provision for income taxes	23,468	24,629
(Provision) benefit for income taxes	(6,041)	(6,328)
Net income (loss)	17,427	18,301
Treasury and Other
Selected business segment financial information
Net interest income	3,206	2,139
Net interest income after provision for loan and lease losses	3,206	2,139
Noninterest income	4,815	5,968
Noninterest expense	(15,972)	(14,478)
Income before provision for income taxes	(7,951)	(6,371)
(Provision) benefit for income taxes	2,034	1,658
Net income (loss)	$ (5,917)	$ (4,713)