Condensed Parent Company Financial Statements - Statements of Cash Flows (Parent Company Only) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Activities
Net income		$ 107,898	$ 199,738	$ 157,870
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of premises, furniture, and equipment		16,451	16,366	15,865
Share-based compensation expense		14,740	13,183	12,062
Tax benefit related to share-based compensation		327	364	258
Net (increase) decrease in other assets		(30,974)	(146,968)	(44,246)
Net (decrease) increase in other liabilities		(30,345)	108,956	(4,346)
Net cash provided by operating activities		135,041	227,109	253,184
Investing Activities
Purchases of premises, furniture, and equipment		(11,279)	(20,330)	(27,800)
Net cash (paid) received for acquisitions			(13,532)
Net cash used in investing activities		(1,095,409)	(1,054,193)	(1,002,386)
Financing Activities
Net proceeds from the issuance of preferred stock	$ 221,187		0	0
Repurchases of common stock		(22,557)	(33,928)	0
Cash dividends paid		(72,585)	(56,540)	(44,293)
Restricted stock activity		(3,036)	(3,830)	(4,421)
Net cash provided by (used in) financing activities		1,778,391	837,047	691,890
Supplemental Disclosures of Cash Flow Information:
Common stock issued for acquisitions, net of issuance costs		71,883	101,496	83,303
Parent Company
Operating Activities
Net income		107,898	199,738	157,870
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed loss (income) of subsidiaries		7,469	7,926	(102,321)
Depreciation of premises, furniture, and equipment		51	51	42
Share-based compensation expense		14,740	13,183	12,062
Tax benefit related to share-based compensation		327	364	258
Net (increase) decrease in other assets		(21,401)	(67,330)	35,981
Net (decrease) increase in other liabilities		(6,185)	49,813	(17,942)
Net cash provided by operating activities		102,899	203,745	85,950
Investing Activities
Purchases of premises, furniture, and equipment		0	0	(61)
Net cash (paid) received for acquisitions		(30,616)	(19,966)	39
Net cash used in investing activities		(30,616)	(19,966)	(22)
Financing Activities
Net proceeds from the issuance of preferred stock		221,187	0	0
Repurchases of common stock		(22,557)
Cash dividends paid		(72,585)	(56,540)	(44,293)
Restricted stock activity		(3,036)	(3,830)	(4,421)
Net cash provided by (used in) financing activities		123,009	(94,298)	(48,714)
Net increase in cash and cash equivalents		195,292	89,481	37,214
Cash and cash equivalents at beginning of year		247,507	158,026	120,812
Cash and cash equivalents at end of year		442,799	247,507	158,026
Supplemental Disclosures of Cash Flow Information:
Common stock issued for acquisitions, net of issuance costs		$ 71,883	$ 101,496	$ 83,303