Debt - Schedule of Debt Instrument Redemption (Details) - Senior Notes [Member] - USD ($)	Mar. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Face amount of debt instrument	$ 500,000,000	$ 500,000,000
Unamortized debt discount	(1,167,000)	(1,235,000)
Unamortized debt issuance costs	(2,590,000)	(2,731,000)
Long-term debt	496,243,000	496,034,000
Senior Notes Due 2024 [Member]
Debt Instrument [Line Items]
Face amount of debt instrument	$ 250,000,000	250,000,000
Stated interest rate	4.40%
Percentage of issuance price	99.883%
Senior Notes Due 2023 [Member]
Debt Instrument [Line Items]
Face amount of debt instrument	$ 250,000,000	$ 250,000,000
Stated interest rate	4.25%
Percentage of issuance price	99.026%

Debt Instrument, Percentage of Issuance Price

No definition available.

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- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Amount, after accumulated amortization, of debt discount.

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- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

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- Details

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