Long-Term Debt (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2016 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)	Apr. 21, 2015 USD ($)	Jun. 30, 2014 USD ($)	Apr. 30, 2010	Apr. 30, 1998 USD ($)
Debt Instrument [Line Items]
Accrued interest expense	$ 12,200		$ 3,600
Potential Increase to Term Loan and Line of Credit				$ 750,000
Debt Issuance Cost		$ 6,500
Interest Expense, Debt	14,280	13,835
Deferred Costs, Current				14,800
Write off of Deferred Debt Issuance Cost		1,600
Senior Debentures						0.500
Market value adjustments on interest rate swap, net of tax	(2,600)	(2,180)
7.25% senior notes due June 2021
Debt Instrument [Line Items]
Debt instrument, face amount	$ 400,000
Debt instrument, stated interest rate percentage	7.25%
Letter Of Credit Sub Facility [Member]
Debt Instrument [Line Items]
Term facility, maximum borrowing capacity				50,000
Amended Credit Agreement [Member]
Debt Instrument [Line Items]
Term facility, maximum borrowing capacity				850,000
Contingent Credit Agreement Revolving Facility [Domain]
Debt Instrument [Line Items]
Term facility, maximum borrowing capacity				550,000
Multi Currency Sub Facility [Member]
Debt Instrument [Line Items]
Term facility, maximum borrowing capacity				$ 100,000
Senior Debentures April 2028 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount							$ 100,000
Term Loan Due March 2019 [Member]
Debt Instrument [Line Items]
Interest Expense, Debt		400
Notes Payable to Banks [Member] | 7.25% senior notes due June 2021
Debt Instrument [Line Items]
Debt instrument, stated interest rate percentage	7.25%
Notes Payable to Banks [Member] | Senior Debentures April 2028 [Member]
Debt Instrument [Line Items]
Debt instrument, stated interest rate percentage	7.55%						7.55%
Interest Rate Swap [Member]
Debt Instrument [Line Items]
Derivative, Notional Amount					$ 500,000
Derivative, Fixed Interest Rate					1.57%
Remaining Balance Of Interest Rate Swap Notional Amount					$ 250,000
Swap [Member]
Debt Instrument [Line Items]
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax	$ (1,700)	(1,400)
December 2017 [Member] | Interest Rate Swap [Member]
Debt Instrument [Line Items]
Quarterly Amortization of Interest Rate Swap Notional Amount					12,500
December 2018 [Member] | Interest Rate Swap [Member]
Debt Instrument [Line Items]
Quarterly Amortization of Interest Rate Swap Notional Amount					$ 25,000
Other Current Assets [Member]
Debt Instrument [Line Items]
Payments of Debt Issuance Costs		$ 6,100
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate Swap [Member]
Debt Instrument [Line Items]
Liability for interest rate swap agreements	$ 8,580		$ 4,370
Guarantor Subsidiaries [Member]
Debt Instrument [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent	100.00%