Income Taxes (Narrative) (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Contingency [Line Items]
Tax benefit related to Tax Cuts and Jobs Act	$ 88,900,000	$ 0	$ 0	$ 88,900,000
Income tax expense (benefit), net benefits for interest and penalties		0	1,600,000	400,000
Accounting Standards Update 2016-09
Income Tax Contingency [Line Items]
Excess tax benefits		$ 100,000	$ 2,500,000	$ 2,200,000