PARENT COMPANY STATEMENTS - CONDENSED STATEMENTS OF CASH FLOWS (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net income	$ 24,283	$ 24,119	$ 24,348	$ 22,983	$ 24,592	$ 22,776	$ 19,670	$ 17,299	$ 95,733	$ 84,337	$ 87,047
Adjustments to net cash from operating activities:
Net cash from operating activities									113,768	87,228	100,039
Cash flows from financing activities:
Repayment of long-term debt									0		(30,928)
Proceeds from (payments on) short-term borrowings										(10,500)	0
Purchase of treasury stock									(559)	(10,547)	(515)
Sales of treasury stock									115	119	118
Net cash from financing activities									651,091	775,342	(48,887)
Net change in cash and cash equivalents									433,313	150,546	(117,541)
Beginning balance				249,927				99,381	249,927	99,381	216,922
Ending balance	683,240				249,927				683,240	249,927	99,381
Reportable Legal Entities | Parent Company
Cash flows from operating activities:
Net income									95,733	84,337	87,047
Adjustments to net cash from operating activities:
Equity in undistributed income of subsidiaries									(53,120)	(53,828)	(32,533)
Other changes									5,177	1,257	3,529
Net cash from operating activities									47,790	31,766	58,043
Cash flows from financing activities:
Repayment of long-term debt										0
Proceeds from (payments on) short-term borrowings									(10,500)
Payments related to equity incentive plans									(1,914)	(2,137)	(2,109)
Purchase of treasury stock									(559)	(10,547)	(515)
Sales of treasury stock									115	119	118
Dividends paid									(34,640)	(30,566)	(29,639)
Net cash from financing activities									(47,498)	(32,631)	(63,073)
Net change in cash and cash equivalents									292	(865)	(5,030)
Beginning balance				$ 3,001				$ 3,866	3,001	3,866	8,896
Ending balance	$ 3,293				$ 3,001				$ 3,293	$ 3,001	$ 3,866