Debt - Narrative (Details)								1 Months Ended
	Jul. 20, 2020 USD ($)	Jun. 28, 2020 USD ($)	May 05, 2020 USD ($)	Apr. 22, 2020 USD ($)	Apr. 06, 2020 USD ($)	Apr. 01, 2020 USD ($) bank	Mar. 18, 2020 USD ($)	May 31, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	[1]
Line of Credit Facility [Line Items]
Expected debt maturities through December 2021		$ 750,000,000
Cash and cash equivalents		857,272,000								$ 145,283,000
Revolving Credit Facility
Line of Credit Facility [Line Items]
Cash and cash equivalents		700,000,000
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
Maximum borrowing capacity						$ 500,000,000
Number of banks in syndicate | bank						8
Repayments of credit facility			$ 250,000,000
Wells Fargo term loan due March 2021 | Term loan | Wells Fargo Bank, NA
Line of Credit Facility [Line Items]
Debt term							364 days
Debt principal							$ 150,000,000	$ 200,000,000	$ 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	$ 150,000,000
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.