Unaudited Quarterly Financial Data - Supplemental Consolidated Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 542,897	$ 513,313	$ 481,301	$ 432,398	$ 405,016	$ 385,271	$ 353,927	$ 320,926	$ 1,969,909		$ 1,465,140		$ 1,193,396
Interest expense	28,437	20,091	14,858	12,535	11,310	11,297	11,231	10,933	75,921		44,771		42,873
Net interest income	514,460	493,222	466,443	419,863	393,706	373,974	342,696	309,993	1,893,988		1,420,369		1,150,523
Provision for credit losses	13,644	17,174	29,080	27,972	22,242	23,522	15,806	30,734	87,870		92,304		106,679
Noninterest income	186,707	210,070	192,689	155,518	152,266	158,778	128,528	117,659	744,984		557,231		456,552
Noninterest expense	307,592	309,445	305,739	265,417	264,015	257,761	251,246	237,633	1,188,193		1,010,655		859,797	[1]
Income before income tax expense	379,931	376,673	324,313	281,992	259,715	251,469	204,172	159,285
Income tax expense	105,000	95,308	77,287	73,966	135,051	97,351	71,656	51,405	351,561	[2]	355,463	[2]	250,333
Net income before noncontrolling interests	274,931	281,365	247,026	208,026	124,664	154,118	132,516	107,880	1,011,348		519,178		390,266
Net income attributable to noncontrolling interests	(8,667)	(6,548)	(9,228)	(13,065)	(7,454)	(5,498)	(9,323)	(6,397)	(37,508)		(28,672)		(7,581)
Net income available to common stockholders	$ 266,264	$ 274,817	$ 237,798	$ 194,961	$ 117,210	$ 148,620	$ 123,193	$ 101,483	$ 973,840	[2]	$ 490,506	[2]	$ 382,685
Earnings per common share—basic (usd per share)	$ 5.01	$ 5.16	$ 4.48	$ 3.69	$ 2.22	$ 2.82	$ 2.34	$ 1.94	$ 18.35	[2]	$ 9.33	[2]	$ 7.37
Earnings per common share—diluted (usd per share)	$ 4.96	$ 5.10	$ 4.42	$ 3.63	$ 2.19	$ 2.79	$ 2.32	$ 1.91	$ 18.11	[2]	$ 9.20	[2]	$ 7.31

[1] Our consolidated statements of income for the year ended December 31, 2016 was modified from prior periods’ presentation to conform to the current period's presentation, which reflects our provision for loan losses and provision for unfunded credit commitments together as our “provision for credit losses”. In prior periods, our provision for unfunded credit commitments were reported separately as a component of noninterest expense.

[2] Included in income tax expense, net income available to common stockholders, earnings per common share-basic and earnings for common share-diluted, for the years ended December 31, 2018 and 2017, are tax benefits recognized associated with the adoption of Accounting Standards Update ("ASU") 2016-09, Improvements to Employee Share-Based Payment Accounting in the first quarter of 2017. This guidance was adopted on a prospective basis with no change to prior period amounts.