Parent Company Cash Flow Statement (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020		Dec. 31, 2019	Dec. 31, 2018
Condensed Financial Statements, Captions [Line Items]
Net income		$ 34,641	$ 34,873	$ 24,902	$ 26,751	$ 47,477	$ 51,845	$ 30,628	$ 35,225	$ 121,167		$ 165,175	$ 121,622
Adjustments to reconcile net income to net cash provided by operating activities
Deferred income tax expense										(17,506)		10,594	(4,497)
Change in other liabilities										76,140		19,283	7,100
Net cash provided by operating activities										64,636		216,522	141,837
Cash flows provided by (used) in investing activities
Net cash used in investing activities										(488,211)		20,160	(387,511)
Cash flows provided by (used in) financing activities
Proceeds from Lines of Credit										0		49,980	0
Repayments of Lines of Credit										0		(49,980)	0
Proceeds from Issuance of Subordinated Long-term Debt										0		49,526	0
Repayments of Subordinated Debt										0		(34,767)	0
Cash received from stock option exercises										197		281	184
Proceeds from shares issued under the direct stock purchase plan										2,132		4,951	2,712
Common dividends paid										(60,840)		(53,274)	(40,167)
Net cash provided by financing activities										1,569,237		(336,163)	283,013
Cash and cash equivalents at beginning of year					150,974				250,455	150,974		250,455	213,116
Cash and cash equivalents at end of period		1,296,636				150,974				1,296,636		150,974	250,455
Payments for Repurchase of Common Stock										(95,091)		0	0
RepaymentsOfJuniorSubordinatedDebt										0		(13,329)	0
Repayments of Long-term Debt										(42,187)
Proceeds from Issuance of Debt												74,867	0
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Investments in subsidiaries	[1]	1,761,383				1,743,435				1,761,383		1,743,435
Net income										121,167		165,175	121,622
Adjustments to reconcile net income to net cash provided by operating activities
Amortization										152		157	54
Deferred income tax expense										284		1,021	49
Change in prepaid income taxes and other assets										(475)	[2]	20,556	135
Change in other liabilities										(169)		(4,613)	6
Deficit (equity) in undistributed income of subsidiaries										40,933		10,641	(53,450)
Net cash provided by operating activities										161,892		192,937	68,416
Cash flows provided by (used) in investing activities
Cash paid for acquisitions, net of cash acquired (2)	[3]											(148,297)	(13,649)
Net cash used in investing activities										0		(148,297)	(13,649)
Cash flows provided by (used in) financing activities
Proceeds from Lines of Credit										0		49,980	0
Repayments of Lines of Credit										0		(49,980)	0
Proceeds from Issuance of Subordinated Long-term Debt										0		49,526	0
Restricted stock awards issued, net of awards surrendered										(1,187)		(1,463)	(1,371)
Cash received from stock option exercises										197		281	184
Proceeds from shares issued under the direct stock purchase plan										2,132		4,951	2,712
Common dividends paid										(60,840)		(53,274)	(40,167)
Net cash provided by financing activities										(196,976)		26,792	(38,642)
Net increase (decrease) in cash and cash equivalents										(35,084)		71,432	16,125
Cash and cash equivalents at beginning of year					$ 135,688				$ 64,256	135,688		64,256	48,131
Cash and cash equivalents at end of period		100,604				135,688				100,604		135,688	64,256
Cash	[4]	100,604				$ 135,688				100,604		135,688
Payments for Repurchase of Common Stock										(95,091)
RepaymentsOfJuniorSubordinatedDebt										0		(13,329)	0
Repayments of Long-term Debt										(42,187)
Proceeds from Issuance of Debt												74,867	0
Reallocation of tax asset from parent to bank subsidiary, noncash adjustment		$ 30,100								30,100
Subordinated Debt [Member] | Parent Company [Member]
Cash flows provided by (used in) financing activities
Repayments of Subordinated Debt										$ 0		$ (34,767)	$ 0

[1] Majority of balance eliminates in consolidation

[2] Reflected in this line for the year ended December 31, 2020 is a noncash adjustment which decreased prepaid income taxes and increased investment in subsidiary by $30.1 million, which represents a reallocation of a tax asset from the parent to the bank subsidiary.

[3] The majority of the net assets acquired at the parent company level represent each of the acquired companies' investments in their wholly owned subsidiaries, which were eliminated in consolidation

[4] Entire balance eliminates in consolidation.