Parent Company Cash Flow Statement (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Net income		$ 47,477	$ 51,845	$ 30,628	$ 35,225	$ 29,934	$ 33,015	$ 31,118	$ 27,555	$ 165,175	$ 121,622	$ 87,204
Adjustments to reconcile net income to net cash provided by operating activities
Deferred income tax expense										10,594	(4,497)	9,211
Change in other liabilities										19,283	7,100	(3,825)
Net cash provided by operating activities										216,522	141,837	130,909
Cash flows provided by (used) in investing activities
Net cash used in investing activities										20,160	(387,511)	(316,769)
Cash flows provided by (used in) financing activities
Proceeds from Lines of Credit										49,980	0	0
Repayments of Lines of Credit										(49,980)	0	0
Proceeds from Debt, Net of Issuance Costs										74,867	0	0
Proceeds from Issuance of Subordinated Long-term Debt										49,526	0	0
Repayments of Subordinated Debt										34,767	0	0
Restricted stock awards issued, net of awards surrendered										(1,463)	(1,371)	(1,422)
Cash received from stock option exercises										281	184	214
Proceeds from shares issued under the direct stock purchase plan										4,951	2,712	1,636
Common dividends paid										(53,274)	(40,167)	(34,045)
Net cash provided by financing activities										(336,163)	283,013	109,881
Net increase (decrease) in cash and cash equivalents										(99,481)	37,339	(75,979)
Cash and cash equivalents at beginning of year					250,455				213,116	250,455	213,116	289,095
Cash and cash equivalents at end of period		150,974				250,455				150,974	250,455	213,116
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Investments in subsidiaries	[1]	1,743,435				1,128,407				1,743,435	1,128,407
Net income										165,175	121,622	87,204
Adjustments to reconcile net income to net cash provided by operating activities
Amortization										157	54	12
Deferred income tax expense										1,021	49	51
Change in prepaid income taxes and other assets										20,556	135	(99)
Change in other liabilities										(4,613)	6	(562)
Deficit (equity) in undistributed income of subsidiaries										10,641	(53,450)	(42,620)
Net cash provided by operating activities										192,937	68,416	43,986
Cash flows provided by (used) in investing activities
Cash paid for acquisitions, net of cash acquired (1)	[2]									(148,297)	(13,649)	(4,834)
Net cash used in investing activities										(148,297)	(13,649)	(4,834)
Cash flows provided by (used in) financing activities
Proceeds from Lines of Credit										49,980	0	0
Repayments of Lines of Credit										(49,980)	0	0
Proceeds from Debt, Net of Issuance Costs										74,867	0	0
Proceeds from Issuance of Subordinated Long-term Debt										49,526	0	0
Restricted stock awards issued, net of awards surrendered										(1,463)	(1,371)	(1,422)
Cash received from stock option exercises										281	184	214
Proceeds from shares issued under the direct stock purchase plan										4,951	2,712	1,636
Common dividends paid										(53,274)	(40,167)	(34,045)
Net cash provided by financing activities										26,792	(38,642)	(33,617)
Net increase (decrease) in cash and cash equivalents										71,432	16,125	5,535
Cash and cash equivalents at beginning of year					$ 64,256				$ 48,131	64,256	48,131	42,596
Cash and cash equivalents at end of period		135,688				64,256				135,688	64,256	48,131
Cash	[3]	$ 135,688				$ 64,256				135,688	64,256
Junior Subordinated Debt [Member] | Parent Company [Member]
Cash flows provided by (used in) financing activities
Repayments of Subordinated Debt										(13,329)	0	0
Subordinated Debt [Member] | Parent Company [Member]
Cash flows provided by (used in) financing activities
Repayments of Subordinated Debt										$ (34,767)	$ 0	$ 0

[1] Majority of balance eliminates in consolidation

[2] The majority of the net assets acquired at the parent company represented each of the acquired companies' investments in their wholly owned subsidiaries, which were eliminated in consolidation at December 31, 2019, 2018, and 2017, respectively.

[3] Entire balance eliminates in consolidation.