Segment Information - Summary of Segment Reporting Information (Detail) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting Information [Line Items]
Net interest income	$ 170,602		$ 150,553		$ 312,120	$ 294,721
Provision for loans losses	45,911		5,417		73,030	10,413
Other income	88,390		39,795		125,196	71,018
Other expense	149,374		100,195		250,507	189,620
Income taxes	11,021		17,529		20,910	34,857
Net income	52,686	$ 40,183	67,207	$ 63,642	92,869	130,849
Total assets (liabilities)	26,234,973		19,882,539		26,234,973	19,882,539
Average assets (liabilities)	24,402,600		19,515,854		21,985,381	19,383,507
Operating Segments [Member] | Community Banking [Member]
Segment Reporting Information [Line Items]
Net interest income	167,703		152,517		308,123	298,407
Provision for loans losses	45,911		5,417		73,030	10,413
Other income	20,301		18,398		39,868	36,050
Other expense	106,477		82,304		186,941	158,298
Income taxes	5,841		17,207		16,191	34,873
Net income	29,775		65,987		71,829	130,873
Total assets (liabilities)	25,924,599		19,735,901		25,924,599	19,735,901
Average assets (liabilities)	24,198,414		19,447,629		21,825,005	19,324,956
Operating Segments [Member] | Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Net interest income	2,246		111		3,195	166
Provision for loans losses	0		0		0	0
Other income	71,013		23,501		92,203	39,607
Other expense	35,261		18,771		56,018	33,613
Income taxes	6,946		1,004		7,219	1,286
Net income	31,052		3,837		32,161	4,874
Total assets (liabilities)	730,637		442,188		730,637	442,188
Average assets (liabilities)	660,483		326,525		513,431	296,008
Other [Member]
Segment Reporting Information [Line Items]
Net interest income	(2,556)		(3,209)		(5,245)	(6,532)
Provision for loans losses	0		0		0	0
Other income	47		53		56	255
Other expense	7,398		143		8,432	(77)
Income taxes	(1,766)		(682)		(2,500)	(1,302)
Net income	(8,141)		(2,617)		(11,121)	(4,898)
Total assets (liabilities)	25,678		16,729		25,678	16,729
Average assets (liabilities)	16,574		5,387		21,756	1,824
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Net interest income	3,209		1,134		6,047	2,680
Provision for loans losses	0		0		0	0
Other income	(2,971)		(2,157)		(6,931)	(4,894)
Other expense	238		(1,023)		(884)	(2,214)
Income taxes	0		0		0	0
Net income	0		0		0	0
Total assets (liabilities)	(445,941)		(312,279)		(445,941)	(312,279)
Average assets (liabilities)	$ (472,871)		$ (263,687)		$ (374,811)	$ (239,281)