Long-Term Debt And Short-Term Borrowings Long-term Debt and Short-term Borrowing (Narrative) (Details) - USD ($)					2 Months Ended
	Sep. 30, 2018	Sep. 30, 2015	Jun. 30, 2015	Apr. 28, 2015	Jun. 30, 2015	Apr. 27, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Current portion of long-term debt			$ 10,000,000		$ 10,000,000		$ 800,000
Restated Credit Agreement
Debt Instrument [Line Items]
Debt Instrument, Required Prepayment, Proceeds From Significant Asset Disposition, Percentage					100.00%
Debt Instrument, Required Prepayment, Proceeds From Significant Asset Disposition, Minimum					$ 10,000,000
Debt Instrument, Required Prepayment, Proceeds From Property Insurance or Condemnation Award, Percentage					100.00%
Debt Instrument, Required Prepayment, Proceeds From Property Insurance or Condemnation Awards, Minimum					$ 10,000,000
Debt Instrument, Required Prepayment, Proceeds From Other Debt Agreements, Percentage					100.00%
Allowed Increase in Consolidated Leverage Ratio after a Material Acquisition					0.50
Permitted Increase in Size of Restated Credit Facility					$ 500,000,000
Restated Credit Agreement | Eurodollar
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate, Term					1 month
Debt Instrument, Basis Spread on Variable Rate			1.50%		1.00%
Restated Credit Agreement | Federal Funds Effective Rate
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate					0.50%
Restated Credit Agreement | Base Rate
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate			0.50%
FIve Year Senior Secured Credit Facility, due April 2020
Debt Instrument [Line Items]
Debt Instrument, Term				5 years
Senior Secured Revolving Credit Facility, due April 2020
Debt Instrument [Line Items]
Letters of credit outstanding			$ 7,000,000		$ 7,000,000
Secured Debt | FIve Year Senior Secured Credit Facility, due April 2020
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				$ 600,000,000
Secured Debt | Senior Secured Revolving Credit Facility, due April 2020
Debt Instrument [Line Items]
Senior Secured Revolving Credit Facility			95,000,000	42,000,000	95,000,000		0
Secured Debt | USD Senior Secured Term Loan A, due April 2020
Debt Instrument [Line Items]
Debt Instrument, Face Amount				300,000,000
Senior Secured Term Loan			295,000,000		295,000,000		0
Current portion of long-term debt			10,000,000		10,000,000
Secured Debt | USD Senior Secured Term Loan A, due May 2018
Debt Instrument [Line Items]
Senior Secured Term Loan			$ 0		0	$ 299,000,000	$ 299,000,000
Revolving Credit Facility | Secured Debt | Senior Secured Revolving Credit Facility, due April 2020
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				300,000,000
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage			0.30%
Amount Available for borrowings under Senior Secured Revolving Credit Facilities			$ 198,000,000		198,000,000
Revolving Credit Facility | Secured Debt | USD Senior Secured Revolving Credit Facility, due May 2018 [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				$ 250,000,000
Minimum | Restated Credit Agreement
Debt Instrument [Line Items]
Base Amount of Dividends and/or Repurchase Shares in an Aggregate Amount in Dollars					$ 25,000,000
Base Amount of Dividends and/or Repurchase Shares in an Aggregate as a Precent of Consolidate Total Assets					1.00%
Consolidated Fixed Charge Coverage Ratio					1.25
Minimum | Revolving Credit Facility | Secured Debt | Senior Secured Revolving Credit Facility, due April 2020
Debt Instrument [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage					0.25%
Maximum | Restated Credit Agreement
Debt Instrument [Line Items]
Aggregate Amount of Investments Allowed per the Restated Credit Agreement in Dollars					$ 500,000,000
Aggregate Amount of Investments Allowed as a Percentage of Consolidated Total Assets					15.00%
Maximum | Revolving Credit Facility | Secured Debt | Senior Secured Revolving Credit Facility, due April 2020
Debt Instrument [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage					0.40%
Scenario, Forecast | Minimum | Secured Debt | USD Senior Secured Term Loan A, due April 2020
Debt Instrument [Line Items]
Debt Instrument, Periodic Payment, Principal, Percentage		5.00%
Scenario, Forecast | Maximum | Secured Debt | USD Senior Secured Term Loan A, due April 2020
Debt Instrument [Line Items]
Debt Instrument, Periodic Payment, Principal, Percentage	12.50%
Less Than Three Point Five to One and Greater Than Two Point Five to One | Restated Credit Agreement
Debt Instrument [Line Items]
Additional Aggregate Amount not to Exceed in any Fiscal Year for Dividends and /or Repurchase Shares					$ 60,000,000
Less Than Two Point Five to One | Restated Credit Agreement
Debt Instrument [Line Items]
Consolidated Leverage Ratio Required for any Additional Amount for Dividends and /or Repurchase Shares					2.50