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Long-Term Debt - 5.00% Senior Notes (Details) - 5.00% Senior Note - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Sep. 09, 2014	Sep. 04, 2014	Jun. 02, 2014
Debt Instrument [Line Items]
Interest rate	5.00%				5.00%
Aggregate principal amount	$ 550,000,000	$ 550,000,000		$ 200,000,000	$ 350,000,000
Additional borrowings discount from face value			1.50%
Unamortized underwriters' fees, discount and debt issuance costs	$ 6,300,000

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Additional borrowings discount from face value

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- Definition

Unamortized Underwriters Fees, Discount, and Debt Issuance Costs

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- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

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-Publisher FASB
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-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

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- Definition

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

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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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.

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