Accounting Policies (Details) - USD ($) $ in Thousands		9 Months Ended
	Jan. 01, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounting Standards Update [Extensible List]		us-gaap:AccountingStandardsUpdate201613Member
Non-cash cumulative effect adjustment to retained earnings, net of tax		$ 441,115	$ 273,400	$ 108,055	$ 177,825	$ 202,722	$ 171,549	$ 51,870	$ (9,233)
Reserve for contract assets and sales-type leases		3,300
Accounts receivable allowance for credit losses		6,600			3,600
Cumulative effect of accounting changes (Note 2)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Non-cash cumulative effect adjustment to retained earnings, net of tax					(1,829)
Accounting Standards Update 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reserve for contract assets and sales-type leases	$ 2,300
Accounts receivable allowance for credit losses	200
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Non-cash cumulative effect adjustment to retained earnings, net of tax		$ 2,000,805	$ 1,854,586	$ 1,705,646	1,595,648	$ 1,505,152	$ 1,396,315	$ 1,270,609	$ 1,167,928
Retained Earnings | Cumulative effect of accounting changes (Note 2)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Non-cash cumulative effect adjustment to retained earnings, net of tax					(1,829)
Retained Earnings | Accounting Standards Update 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Non-cash cumulative effect adjustment to retained earnings, tax	$ 600
Retained Earnings | Accounting Standards Update 2016-13 | Cumulative effect of accounting changes (Note 2)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Non-cash cumulative effect adjustment to retained earnings, net of tax					$ 1,800