Business Segments (Operating Results and Other Key Financial Measures) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Total Segment Reporting Information
Interest income	$ 422,185	$ 339,910	$ 1,194,369	$ 965,354
Charge for funds used	(215,643)	(132,639)	(594,980)	(378,459)
Interest spread on funds used	206,542	207,271	599,389	586,895
Interest expense	(73,465)	(36,755)	(177,277)	(99,986)
Credit on funds provided	215,643	132,639	594,980	378,459
Interest spread on funds provided (used)	142,178	95,884	417,703	278,473
Net interest income before provision for credit losses	348,720	303,155	1,017,092	865,368
Provision for credit losses	10,542	12,996	46,296	30,749
Noninterest income	46,502	49,470	169,214	212,542
Noninterest expense	179,815	164,345	526,369	486,188
Segment income (loss) before income taxes	204,865	175,284	613,641	560,973
Segment net income	171,302	132,660	530,683	420,726
Segment assets	39,073,106	36,307,966	39,073,106	36,307,966	$ 37,150,249
Retail Banking
Total Segment Reporting Information
Interest income	120,449	93,714	335,967	263,491
Charge for funds used	(65,499)	(37,979)	(171,687)	(98,856)
Interest spread on funds used	54,950	55,735	164,280	164,635
Interest expense	(41,207)	(20,090)	(98,138)	(54,650)
Credit on funds provided	168,529	111,812	472,426	320,452
Interest spread on funds provided (used)	127,322	91,722	374,288	265,802
Net interest income before provision for credit losses	182,272	147,457	538,568	430,437
Provision for credit losses	705	2,058	7,212	1,772
Noninterest income	13,137	16,068	72,170	43,273
Noninterest expense	87,341	80,614	255,453	233,408
Segment income (loss) before income taxes	107,363	80,853	348,073	238,530
Segment net income	76,732	47,541	249,196	140,255
Segment assets	10,194,291	8,877,186	10,194,291	8,877,186
Commercial Banking
Total Segment Reporting Information
Interest income	271,760	218,397	772,904	616,689
Charge for funds used	(139,986)	(87,071)	(378,134)	(229,330)
Interest spread on funds used	131,774	131,326	394,770	387,359
Interest expense	(13,808)	(5,943)	(34,622)	(16,225)
Credit on funds provided	31,804	12,770	87,980	37,436
Interest spread on funds provided (used)	17,996	6,827	53,358	21,211
Net interest income before provision for credit losses	149,770	138,153	448,128	408,570
Provision for credit losses	9,837	10,938	39,084	28,977
Noninterest income	27,861	30,316	86,043	82,634
Noninterest expense	53,233	46,977	174,959	145,901
Segment income (loss) before income taxes	114,561	110,554	320,128	316,326
Segment net income	81,969	65,311	229,541	186,873
Segment assets	22,930,768	21,216,848	22,930,768	21,216,848
Other
Total Segment Reporting Information
Interest income	29,976	27,799	85,498	85,174
Charge for funds used	(10,158)	(7,589)	(45,159)	(50,273)
Interest spread on funds used	19,818	20,210	40,339	34,901
Interest expense	(18,450)	(10,722)	(44,517)	(29,111)
Credit on funds provided	15,310	8,057	34,574	20,571
Interest spread on funds provided (used)	(3,140)	(2,665)	(9,943)	(8,540)
Net interest income before provision for credit losses	16,678	17,545	30,396	26,361
Provision for credit losses	0	0	0	0
Noninterest income	5,504	3,086	11,001	86,635
Noninterest expense	39,241	36,754	95,957	106,879
Segment income (loss) before income taxes	(17,059)	(16,123)	(54,560)	6,117
Segment net income	12,601	19,808	51,946	93,598
Segment assets	$ 5,948,047	$ 6,213,932	$ 5,948,047	$ 6,213,932