Unaudited Quarterly Financial Data - Supplemental Consolidated Financial Information (Details) - USD ($) $ / shares in Units, $ 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
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 588,735	$ 583,892	$ 585,767	$ 551,014	$ 542,897	$ 513,313	$ 481,301	$ 432,398	$ 2,309,408	$ 1,969,909	$ 1,465,140
Interest expense	55,067	63,248	56,364	38,128	28,437	20,091	14,858	12,535	212,807	75,921	44,771
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
Provision for credit losses	17,383	36,536	23,946	28,551	13,644	17,174	29,080	27,972	106,416	87,870	92,304
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	368,877	386,793	455,685	399,047	379,931	376,673	324,313	281,992
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 before noncontrolling interests	274,816	281,718	336,571	291,612	274,931	281,365	247,026	208,026	1,184,717	1,011,348	519,178
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
Earnings per common share—basic (usd per share)	$ 5.10	$ 5.19	$ 6.12	$ 5.49	$ 5.01	$ 5.16	$ 4.48	$ 3.69	$ 21.90	$ 18.35	$ 9.33
Earnings per common share—diluted (usd per share)	$ 5.06	$ 5.15	$ 6.08	$ 5.44	$ 4.96	$ 5.10	$ 4.42	$ 3.63	$ 21.73	$ 18.11	$ 9.20