Debt (Outstanding Debt Including Capital Leases and Lease Financing Obligations) (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Outstanding debt
Capital lease and lease financing obligations	$ 43,440	49,761
Total debt and lease obligations	839,440	873,763
Less discount and debt issuance costs	(11,224)	(12,194)
Total outstanding debt, net	$ 828,216	861,569
Senior Notes [Member]
Debt Instrument [Line Items]
Weighted average coupon interest rate	5.88%
Maturity date	Aug. 01, 2022
Outstanding debt	$ 300,000	300,000
Capital Lease and Lease Financing Obligations [Member]
Debt Instrument [Line Items]
Weighted average coupon interest rate	3.45%
Maturity date decription	2016 - 2025
Capital lease and lease financing obligations	$ 43,440	49,761
Unsecured Credit Facility [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Weighted average coupon interest rate	2.01%
Maturity date	Dec. 17, 2019
Outstanding debt	$ 196,000	224,002
Unsecured Credit Facility [Member] \| Term Loan I [Member]
Debt Instrument [Line Items]
Weighted average coupon interest rate	1.95%
Maturity date	Dec. 17, 2020
Outstanding debt	$ 150,000	150,000
Unsecured Credit Facility [Member] \| Term Loan II [Member]
Debt Instrument [Line Items]
Weighted average coupon interest rate	1.95%
Maturity date	Apr. 27, 2021
Outstanding debt	$ 150,000	$ 150,000
Unsecured Credit Facility, Senior Notes, Capital Lease and Lease Financing Obligations [Member]
Debt Instrument [Line Items]
Weighted average coupon interest rate	3.44%

Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Sum of the carrying values as of the balance sheet date of all debt, including all short-term borrowings, long-term debt, and capital lease obligations.

+ References

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

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ 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.

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- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

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- Definition

Description of the maturity date of the debt instrument including whether the debt matures serially and, if so, a brief description of the serial maturities.

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- Definition

Amount, after accumulated amortization, of debt discount (premium).

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- Definition

Weighted average interest rate of debt outstanding.

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- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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