Business Combination - Revenue and Expenses from SVB Leerink (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Net interest income	$ 533,668	$ 520,644	$ 529,403	$ 512,886	$ 514,460	$ 493,222	$ 466,443	$ 419,863	$ 2,096,601	$ 1,893,988	$ 1,420,369
Noninterest income	313,344	294,009	333,750	280,376	186,707	210,070	192,689	155,518	1,221,479	744,984	557,231
Noninterest expense	460,752	391,324	383,522	365,664	307,592	309,445	305,739	265,417	1,601,262	1,188,193	1,010,655
Income before income tax expense									1,610,402	1,362,909	874,641
Income tax expense	94,061	105,075	119,114	107,435	105,000	95,308	77,287	73,966	425,685	351,561	355,463
Net income attributable to noncontrolling interests	11,960	14,437	18,584	2,880	8,667	6,548	9,228	13,065	47,861	37,508	28,672
Net income available to common stockholders	$ 262,856	$ 267,281	$ 317,987	$ 288,732	$ 266,264	$ 274,817	$ 237,798	$ 194,961	1,136,856	$ 973,840	$ 490,506
SVB Leerink
Business Acquisition [Line Items]
Net interest income									1,252
Noninterest income									265,841
Noninterest expense									252,678
Income before income tax expense									14,415
Income tax expense									3,566
Net income attributable to noncontrolling interests									1,325
Net income available to common stockholders									$ 9,524