Reportable Operating Segments - Selected Business Segment Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Selected business segment financial information
Net interest income (expense)	$ 120,427		$ 118,942	$ 237,739	$ 231,553
Provision for loan and lease losses	(1,900)		(2,250)	(2,600)	(4,850)
Net interest income after provision for loan and lease losses	118,527		116,692	235,139	226,703
Noninterest income	46,371		52,115	119,890	107,713
Noninterest expense	(78,473)		(81,215)	(163,537)	(159,930)
Income before income taxes	86,425		87,592	191,492	174,486
Provision for income taxes	(31,565)		(33,034)	(71,101)	(65,806)
Net income	54,860	$ 65,531	54,558	120,391	108,680
Retail Banking
Selected business segment financial information
Net interest income (expense)	103,771		99,667	206,196	197,826
Provision for loan and lease losses	(696)		(1,060)	(952)	(2,285)
Net interest income after provision for loan and lease losses	103,075		98,607	205,244	195,541
Noninterest income	22,525		24,029	46,155	48,542
Noninterest expense	(54,266)		(51,007)	(109,402)	(101,829)
Income before income taxes	71,334		71,629	141,997	142,254
Provision for income taxes	(26,067)		(27,109)	(53,055)	(53,640)
Net income	45,267		44,520	88,942	88,614
Commercial Banking
Selected business segment financial information
Net interest income (expense)	28,212		31,947	55,805	59,104
Provision for loan and lease losses	(1,204)		(1,190)	(1,648)	(2,565)
Net interest income after provision for loan and lease losses	27,008		30,757	54,157	56,539
Noninterest income	16,671		15,811	33,019	35,129
Noninterest expense	(13,106)		(14,503)	(24,884)	(27,088)
Income before income taxes	30,573		32,065	62,292	64,580
Provision for income taxes	(11,145)		(12,154)	(23,241)	(24,344)
Net income	19,428		19,911	39,051	40,236
Treasury and Other
Selected business segment financial information
Net interest income (expense)	(11,556)		(12,672)	(24,262)	(25,377)
Net interest income after provision for loan and lease losses	(11,556)		(12,672)	(24,262)	(25,377)
Noninterest income	7,175		12,275	40,716	24,042
Noninterest expense	(11,101)		(15,705)	(29,251)	(31,013)
Income before income taxes	(15,482)		(16,102)	(12,797)	(32,348)
Provision for income taxes	5,647		6,229	5,195	12,178
Net income	$ (9,835)		$ (9,873)	$ (7,602)	$ (20,170)