Unaudited Quarterly Financial Data Supplemental Consolidated Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 405,016	$ 385,271	$ 353,927	$ 320,926	$ 307,333	$ 300,413	$ 293,992	$ 291,658	$ 1,465,140		$ 1,193,396		$ 1,046,765
Interest expense	11,310	11,297	11,231	10,933	10,728	11,252	10,656	10,237	44,771		42,873		40,340
Net interest income	393,706	373,974	342,696	309,993	296,605	289,161	283,336	281,421	1,420,369		1,150,523		1,006,425
Provision for loan losses	22,242	23,522	15,806	30,734	16,454	20,004	36,746	33,475	92,304		106,679	[1]	95,683	[1]
Noninterest Income	152,266	158,778	128,528	117,659	113,502	144,140	112,776	86,134	557,231		456,552		472,794
Noninterest expense	264,015	257,761	251,246	237,633	235,186	220,773	199,939	203,899	1,010,655		859,797	[1]	779,962	[1]
Income before income tax expense	259,715	251,469	204,172	159,285	158,467	192,524	159,427	130,181
Income tax expense	135,051	97,351	71,656	51,405	54,825	76,877	65,047	53,584	355,463	[2]	250,333		228,754
Net income before noncontrolling interests	124,664	154,118	132,516	107,880	103,642	115,647	94,380	76,597	519,178		390,266		374,820
Net income attributable to noncontrolling interests	(7,454)	(5,498)	(9,323)	(6,397)	(4,176)	(4,566)	(1,416)	2,577	(28,672)		(7,581)		(30,916)
Net income available to common stockholders	$ 117,210	$ 148,620	$ 123,193	$ 101,483	$ 99,466	$ 111,081	$ 92,964	$ 79,174	$ 490,506	[2]	$ 382,685		$ 343,904
Earnings per common share—basic, in dollars per share	$ 2.22	$ 2.82	$ 2.34	$ 1.94	$ 1.91	$ 2.13	$ 1.79	$ 1.53	$ 9.33	[2]	$ 7.37		$ 6.70
Earnings per common share—diluted, in dollars per share	$ 2.19	$ 2.79	$ 2.32	$ 1.91	$ 1.89	$ 2.12	$ 1.78	$ 1.52	$ 9.20	[2]	$ 7.31		$ 6.62

[1] Our consolidated statements of income for the years ended December 31, 2016 and 2015 were 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 year ended December 31, 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.