Debt (Outstanding Debt Including Capital Leases) (Details) - USD ($) $ in Thousands	1 Months Ended	9 Months Ended
Dec. 31, 2016	Sep. 30, 2017
Debt Instrument [Line Items]
Total debt and lease obligations	$ 977,708	$ 1,109,725
Less discount and debt issuance costs	(11,882)	(10,410)
Total outstanding debt, net	965,826	$ 1,099,315
Senior Notes.
Debt Instrument [Line Items]
Weighted average coupon interest rate		5.88%
Maturity date		Aug. 01, 2022
Outstanding debt	300,000	$ 300,000
Lenexa Mortgage
Debt Instrument [Line Items]
Weighted average coupon interest rate		4.10%
Maturity date		May 01, 2022
Outstanding debt		$ 1,882
Capital Lease and Lease Financing Obligations [Member]
Debt Instrument [Line Items]
Weighted average coupon interest rate		3.87%
Maturity date description		2017 - 2025
Capital Lease and Lease Financing Obligations	$ 38,708	$ 28,843
Unsecured Credit Facility
Debt Instrument [Line Items]
Weighted average coupon interest rate		3.63%
Unsecured Credit Facility \| Revolving Credit Facility
Debt Instrument [Line Items]
Weighted average coupon interest rate		2.78%
Maturity date	Dec. 17, 2020	Dec. 17, 2020
Outstanding debt	$ 139,000	$ 279,000
Unsecured Credit Facility \| Term Loan I [Member]
Debt Instrument [Line Items]
Weighted average coupon interest rate		2.74%
Maturity date		Dec. 17, 2021
Outstanding debt	300,000	$ 300,000
Unsecured Credit Facility \| Term Loan II [Member]
Debt Instrument [Line Items]
Weighted average coupon interest rate		2.74%
Maturity date		Apr. 27, 2022
Outstanding debt	$ 200,000	$ 200,000

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.

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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.

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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.

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

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

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Weighted average interest rate of debt outstanding.

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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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