Fair Value of Financial Instruments (Schedule of Summarized Financial Information of Equity Method Investments) (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
Schedule of Equity Method Investments [Line Items]
Total current assets	$ 2,359,015				$ 2,173,559				$ 2,359,015	$ 2,173,559
Total assets	5,227,849				4,997,006				5,227,849	4,997,006	$ 4,440,000
Current liabilities	1,415,199				1,219,126				1,415,199	1,219,126
Total liabilities	3,222,324				3,205,315				3,222,324	3,205,315
Revenue	1,636,800	$ 1,698,300	$ 1,569,300	$ 1,416,600	1,709,300	$ 2,016,600	$ 1,939,000	$ 1,518,300	6,320,975	7,183,188	6,909,417
Net income	112,900	$ 116,900	$ 56,800	$ 36,100	100,700	$ 130,100	$ 120,200	$ 43,100	322,699	394,096	259,231
Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule of Equity Method Investments [Line Items]
Total current assets	160,300				144,500				160,300	144,500
Long-term assets	1,395,400				1,359,900				1,395,400	1,359,900
Total assets	1,555,700				1,504,400				1,555,700	1,504,400
Current liabilities	56,000				34,900				56,000	34,900
Long-term liabilities	1,024,500				978,600				1,024,500	978,600
Total liabilities	$ 1,080,500				$ 1,013,500				1,080,500	1,013,500
Revenue									169,200	152,400	145,800
Net income									$ 94,700	$ 82,800	$ 72,400