Fair Value Measurements (Carrying Amounts and Fair Value of Current and Long-term Debt) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Senior Notes \| 2021 Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Stated percentage	6.75%
Senior Notes \| 2025 Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Stated percentage	6.875%
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Current and long-term debt	$ 1,323,317	$ 1,280,133
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Current and long-term debt	$ 1,379,850	$ 1,317,222

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13433-108611

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13476-108611

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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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- 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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