Parent Company Statement of Cash Flows (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	Dec. 31, 2017
Net Income (Loss) Attributable to Parent	$ 45,200	$ 30,846	$ 29,505	$ 22,372	$ 23,936	$ 31,146	$ 22,163	$ 25,455	$ 127,923	$ 102,700	$ 110,387
Share-based Payment Arrangement, Noncash Expense									7,272	6,324	5,063
Debt and Equity Securities, Unrealized Gain (Loss)									245	(4,204)	(3,267)
Increase (Decrease) in Other Operating Assets									(9,216)	(12,530)	(9,904)
Increase (Decrease) in Other Operating Liabilities									(6,302)	(3,781)	5,131
Net cash provided by operating activities									111,646	111,626	131,994
Payments to Acquire Businesses, Gross									0	(28,630)	(30,684)
Other investing activities, net									(2,621)	5,723	60
Net cash used in investing activities									(455,902)	60,079	45,445
Proceeds from Issuance of Long-term Debt									0	50,000	50,000
Repayments of Long-term Debt									170,529		150,197
Payments Related to Tax Withholding for Share-based Compensation									1,002	827	610
Net cash (used in) provided by financing activities									554,774	(178,963)	(179,337)
Increase (decrease) in cash and cash equivalents									210,518	(7,258)	(1,898)
Treasury Stock, Common [Member]
Payments for Repurchase of Equity									7,507	40,535	5,784
Parent Company
Net Income (Loss) Attributable to Parent									127,923	102,700	110,387
Undistributed Losses Of Subsidiaries									41,730	16,828	14,270
Compensation expense for issuance of treasury shares to directors									1,274	1,325	1,109
Share-based Payment Arrangement, Noncash Expense									5,998	4,999	3,954
Increase (Decrease) in Other Operating Assets									(6,632)	8,544	2,073
Increase (Decrease) in Other Operating Liabilities									(6,325)	10,006	(163)
Net cash provided by operating activities									94,017	89,454	95,677
Net cash used in investing activities									(2,621)	(22,907)	(30,624)
Payments of Dividends									70,353	69,113	63,013
Proceeds from Issuance of Long-term Debt									172,620	50,000	0
Repayments of Long-term Debt									(10,000)	(7,500)	0
Cash Payment For Fractional Shares									3	3	4
Payments Related to Tax Withholding for Share-based Compensation									(1,002)	(827)	(610)
Net cash (used in) provided by financing activities									83,755	(67,978)	(69,411)
Increase (decrease) in cash and cash equivalents									175,151	(1,431)	(4,358)
Cash	$ 248,814				$ 73,663				$ 248,814	$ 73,663	$ 75,094	$ 79,452