Business and Summary of Significant Accounting Policies - Impact of Adoption on Financials (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018	Dec. 31, 2015
Condensed Consolidated Statements of Earnings
Revenues	$ 993,184	$ 953,071	$ 927,859	$ 954,809	$ 884,627	$ 838,883	$ 815,644	$ 844,554	$ 3,828,923	$ 3,383,708	$ 3,207,716
Operating Expenses									1,618,423	1,403,985	1,351,785
Operating profit									289,608	254,699	242,676
Earnings (Loss) Before Income Tax (Benefit) Expense:	82,057	53,415	49,980	66,752	60,738	39,221	56,995	82,623	252,204	239,577	218,422
Income Tax Expense (Benefit)									55,994	(52,959)	79,139
Net Earnings	61,743	$ 43,720	$ 38,501	$ 52,246	177,560	$ 25,341	$ 36,335	$ 53,300	196,210	292,536	139,283
Condensed Consolidated Balance Sheets
Deferred Income Taxes Payable	267,500				222,592				267,500	222,592
Contract with Customer, Liability	80,579				68,060				80,579	68,060
Total Liabilities	1,065,984				964,260				1,065,984	964,260
Retained Earnings	2,005,344				1,819,524				2,005,344	1,819,524
Total Shareholders’ Equity	1,760,708				1,728,004				1,760,708	1,728,004	1,481,598		$ 1,366,618
Total Liabilities & Shareholders’ Equity	2,826,692				$ 2,692,264				2,826,692	2,692,264
Condensed Comprehensive Statements of Income
Comprehensive Income									194,349	293,841	139,269
Franchise Royalties and Fees
Condensed Consolidated Statements of Earnings
Revenues									44,815	$ 48,278	$ 58,350
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Condensed Consolidated Statements of Earnings
Operating Expenses									1,611,210
Operating profit									288,250
Earnings (Loss) Before Income Tax (Benefit) Expense:									250,846
Income Tax Expense (Benefit)									55,661
Net Earnings									195,185
Condensed Consolidated Balance Sheets
Deferred Income Taxes Payable	267,790								267,790
Contract with Customer, Liability	79,585								79,585
Total Liabilities	1,065,280								1,065,280
Retained Earnings	2,006,048								2,006,048
Total Shareholders’ Equity	1,761,412								1,761,412
Total Liabilities & Shareholders’ Equity	2,826,692								2,826,692
Condensed Comprehensive Statements of Income
Comprehensive Income									193,324
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Franchise Royalties and Fees
Condensed Consolidated Statements of Earnings
Revenues									36,245
Accounting Standards Update 2014-09, Revenue From Contracts With Customers | Difference between Revenue Guidance in Effect before and after Topic 606
Condensed Consolidated Statements of Earnings
Operating Expenses									7,213
Operating profit									1,358
Earnings (Loss) Before Income Tax (Benefit) Expense:									1,358
Income Tax Expense (Benefit)									333
Net Earnings									1,025
Condensed Consolidated Balance Sheets
Deferred Income Taxes Payable	(290)								(290)
Contract with Customer, Liability	994								994
Total Liabilities	704								704
Retained Earnings	(704)								(704)			$ (2,400)
Total Shareholders’ Equity	(704)								(704)
Total Liabilities & Shareholders’ Equity	$ 0								0
Condensed Comprehensive Statements of Income
Comprehensive Income									1,025
Accounting Standards Update 2014-09, Revenue From Contracts With Customers | Difference between Revenue Guidance in Effect before and after Topic 606 | Franchise Royalties and Fees
Condensed Consolidated Statements of Earnings
Revenues									$ 8,570