Long-Term Debt, Net of Current (Narrative) (Details) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	Apr. 30, 2010	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2018	Dec. 31, 2017	Jul. 31, 2016	Dec. 31, 2015	Apr. 30, 2015	Apr. 21, 2015	Dec. 31, 2014	Apr. 30, 1998
Debt Instrument [Line Items]
Accrued interest expense		$ 3,600,000		$ 3,600,000					$ 3,600,000
Potential increase to term loan and line of credit										$ 750,000,000
Term loan borrowings		1,653,178,000		1,653,178,000					1,364,008,000
Debt issuance costs			$ 6,500,000
Debt issuance costs expensed		18,401,000	17,480,000	32,681,000	$ 31,315,000
Debt issuance costs capitalized				0	6,452,000
Unamortized costs related to previously recorded debt issuance costs											$ 14,800,000
Unamortized debt issuance costs written off					1,600,000
Market value adjustments on interest rate swap, net of tax		(439,000)	1,113,000	(3,038,000)	(1,067,000)
Interest Rate Swap [Member]
Debt Instrument [Line Items]
Swaps notional amount												$ 500,000,000
Swaps fixed interest rate												1.57%
Interest Rate Swap [Member] | Forecast [Member]
Debt Instrument [Line Items]
Quarterly amortization of interest rate swap notional amount						$ 25,000,000	$ 12,500,000
Remaining notional amount of swaps						$ 250,000,000
Swap [Member]
Debt Instrument [Line Items]
Deferred taxes on interest rate swaps		(300,000)	700,000	(1,900,000)	(700,000)
Fair Value, Measurements, Recurring [Member] | Interest Rate Swap [Member]
Debt Instrument [Line Items]
Liability for interest rate swap agreements		9,291,000		9,291,000					4,370,000
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		9,291,000		9,291,000					4,370,000
Minimum [Member]
Debt Instrument [Line Items]
Valid consents tendered, percentage of outstanding debentures	50.00%
Other Current Assets [Member]
Debt Instrument [Line Items]
Debt issuance costs capitalized					$ 6,100,000
7.25% senior notes due June 2021
Debt Instrument [Line Items]
Debt instrument, face amount		$ 400,000,000		$ 400,000,000
Debt instrument, stated interest rate percentage		7.25%		7.25%
Letter Of Credit Sub Facility [Member]
Debt Instrument [Line Items]
Term facility, maximum borrowing capacity										50,000,000
Amended Credit Agreement [Member]
Debt Instrument [Line Items]
Term facility, maximum borrowing capacity										850,000,000
Amended Credit Agreement [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Term loan borrowings								$ 525,000,000
Contingent Credit Agreement Revolving Facility [Member]
Debt Instrument [Line Items]
Term facility, maximum borrowing capacity										550,000,000
Multi Currency Sub Facility [Member]
Debt Instrument [Line Items]
Term facility, maximum borrowing capacity										$ 100,000,000
Senior Debentures April 2028 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount													$ 100,000,000
Term Loan Due March 2019 [Member]
Debt Instrument [Line Items]
Debt issuance costs expensed			$ 400,000
Notes [Member] | 7.25% senior notes due June 2021
Debt Instrument [Line Items]
Debt instrument, stated interest rate percentage		7.25%		7.25%
Term loan borrowings		$ 393,000,000		$ 393,000,000					393,000,000
Notes [Member] | Senior Debentures April 2028 [Member]
Debt Instrument [Line Items]
Debt instrument, stated interest rate percentage		7.55%		7.55%									7.55%
Term loan borrowings		$ 59,645,000		$ 59,645,000					$ 59,645,000