Related Party Transactions (Subcontracting Arrangements and Other Transactions) (Narrative) (Details) $ in Millions	3 Months Ended
Mar. 31, 2018 USD ($) employee	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
Management [Member] \| Subcontracting Arrangements [Member] \| Related Contractor or Supplier [Member]
Related Party Transaction [Line Items]
Number of additional management employees, subcontracting arrangement \| employee	2
Payments or expenses, related party	$ 5.0	$ 0.6
Payables, related party	1.0		$ 2.0
Management [Member] \| Service Agreements [Member]
Related Party Transaction [Line Items]
Payments or expenses, related party	9.0	6.6
Payables, related party	1.4		5.2
Management [Member] \| Lease Agreements [Member]
Related Party Transaction [Line Items]
Payments or expenses, related party	7.5	12.7
Payables, related party	3.4		0.1
Executive Officers [Member] \| Employee Leasing Arrangements [Member] \| Related Customer [Member]
Related Party Transaction [Line Items]
Charges, related party	0.2	0.2
Receivables, related party	0.2		0.2
Executive Officers [Member] \| Service Agreements [Member] \| Related Customer [Member]
Related Party Transaction [Line Items]
Revenue, related parties	0.3	0.2
Receivables, related party	0.3		$ 0.3
Chairman, Board of Directors [Member] \| Lease Agreements [Member] \| Aircraft [Member]
Related Party Transaction [Line Items]
Payments or expenses, related party	$ 0.5	$ 0.5

Number of persons employed by the Entity

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Amount for accounts payable to related parties.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition

Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

+ References

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Reflects the sum of all other revenue and income realized from sales and other transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party during the period.

+ References

No definition available.

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Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.

+ References

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