Debt - Narrative (Details)									1 Months Ended
	Oct. 22, 2020 USD ($)	Sep. 27, 2020 USD ($)	Jul. 20, 2020 USD ($)	May 05, 2020 USD ($)	Apr. 22, 2020 USD ($)	Apr. 06, 2020 USD ($)	Apr. 01, 2020 USD ($) bank	Mar. 18, 2020 USD ($)	May 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	[1]
Line of Credit Facility [Line Items]
Expected debt maturities through December 2021		$ 760,000,000
Cash and cash equivalents		782,679,000								$ 145,283,000
Revolving Credit Facility
Line of Credit Facility [Line Items]
Cash and cash equivalents		782,679,000
Committed availability under credit facilities		$ 500,000,000
Revolving Credit Facility | Wells Fargo Bank, NA
Line of Credit Facility [Line Items]
Proceeds from lines of credit							$ 250,000,000
Repayments of credit facility				$ 250,000,000
Maximum borrowing capacity							$ 500,000,000
Number of banks in syndicate | bank							8
Wells Fargo term loan due March 2021 | Term loan | Wells Fargo Bank, NA
Line of Credit Facility [Line Items]
Debt term								364 days
Repayments of term loan			$ 150,000,000
Debt principal								$ 150,000,000	$ 200,000,000
Debt instrument term extension period									364 days
Wells Fargo term loan due March 2021 | Term loan | Wells Fargo Bank, NA | Subsequent Event
Line of Credit Facility [Line Items]
Repayments of term loan	$ 200,000,000
Wells Fargo term loan due March 2021 | Term loan | Wells Fargo Bank, NA | LIBOR
Line of Credit Facility [Line Items]
Basis points (percent)		1.125%
U.S. Bank term loan due March 2021 | Term loan | U.S. Bank, NA
Line of Credit Facility [Line Items]
Debt term						364 days
Debt principal						$ 100,000,000
Repayments of commercial paper							$ 85,000,000
U.S. Bank term loan due March 2021 | Term loan | U.S. Bank, NA | LIBOR
Line of Credit Facility [Line Items]
Basis points (percent)		1.25%
3.125% debentures due May 2030
Line of Credit Facility [Line Items]
Interest rate (percent)		3.125%
3.125% debentures due May 2030 | Notes
Line of Credit Facility [Line Items]
Debt principal					$ 600,000,000
Interest rate (percent)					3.125%
Proceeds from debentures issued					$ 594,200,000

[1] The year-end condensed consolidated balance sheet data was derived from audited financial statements, but does not include all disclosures required by accounting principles generally accepted in the United States of America.