Significant Accounting Policies (Changes in Goodwill) (Details) - USD ($)	3 Months Ended		12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019		Dec. 31, 2018
Accounting Policies [Abstract]
Goodwill and intangible asset impairment	$ 0	$ 0
Goodwill [Roll Forward]
Beginning balance			$ 1,802,670,000		$ 1,614,494,000
Additions			0		188,176,000
Other			4,262,000	[1]	0
Ending balance	$ 1,798,408,000	$ 1,802,670,000	$ 1,798,408,000		$ 1,802,670,000

[1] Amounts relate to adjustments to the purchase price allocation associated with 2018 business combinations. See Note 4 for more information regarding the Company's acquisitions.