Basis and Summary of Significant Accounting Policies - Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Jan. 01, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues		$ 927,859	$ 815,644	$ 1,882,668	$ 1,660,198
Operating Expenses		388,337	330,548	778,569	659,373
OPERATING PROFIT		73,931	61,006	143,995	147,495
EARNINGS BEFORE INCOME TAXES		49,980	56,995	116,732	139,618
INCOME TAXES		11,479	20,660	25,985	49,983
NET EARNINGS		38,501	36,335	90,747	89,635
Deferred Income Taxes Payable		257,620		257,620		$ 222,592
Customer Deposits and Advance Payments		72,613		72,613		68,060
Total Liabilities		874,137		874,137		964,260
Retained Earnings		(1,904,309)		(1,904,309)		(1,819,524)
Total Shareholders’ Equity		1,744,813		1,744,813		1,728,004
Total Liabilities & Shareholders’ Equity		2,618,950		2,618,950		$ 2,692,264
Comprehensive Income		37,966	36,781	89,735	90,284
ASU 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred Revenue, Amortization Period	5 years
Balance Without ASC 606 Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Expenses		386,495		774,891
OPERATING PROFIT		73,726		143,531
EARNINGS BEFORE INCOME TAXES		49,775		116,268
INCOME TAXES		11,429		25,871
NET EARNINGS		38,347		90,396
Deferred Income Taxes Payable		258,129		258,129
Customer Deposits and Advance Payments		70,725		70,725
Total Liabilities		872,758		872,758
Retained Earnings		(1,905,688)		(1,905,688)
Total Shareholders’ Equity		1,746,192		1,746,192
Total Liabilities & Shareholders’ Equity		2,618,950		2,618,950
Comprehensive Income		37,812		89,384
Effect of Change Higher/(Lower) | ASU 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Expenses		1,842		3,678
OPERATING PROFIT		205		464
EARNINGS BEFORE INCOME TAXES		205		464
INCOME TAXES		50		114
NET EARNINGS		154		351
Deferred Income Taxes Payable		(509)		(509)
Customer Deposits and Advance Payments	$ 2,400	1,888		1,888
Total Liabilities		1,379		1,379
Retained Earnings	$ 2,400	1,379		1,379
Total Shareholders’ Equity		(1,379)		(1,379)
Total Liabilities & Shareholders’ Equity		0		0
Comprehensive Income		154		351
Franchise Royalties and Fees
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues		12,125	$ 12,824	24,987	$ 27,025
Franchise Royalties and Fees | Balance Without ASC 606 Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues		10,078		20,844
Franchise Royalties and Fees | Effect of Change Higher/(Lower) | ASU 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues		$ 2,047		$ 4,143