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Long-Term Debt (Details) $ in Thousands					12 Months Ended
	Sep. 22, 2017 Rate	Aug. 22, 2017 Rate	Feb. 21, 2017 USD ($) Rate	Aug. 05, 2016 Rate	Dec. 31, 2017 USD ($) Rate	Dec. 31, 2016 USD ($)	Jun. 05, 2015 USD ($)
Debt Instrument [Line Items]
Secured Debt					$ 588,000	$ 656,000
Unamortized Debt Issuance Expense					(12,787)	(15,645)
Long-term Debt					575,213	640,355
Creditfacilityamendmentcosts					$ 3,300	900
Line of Credit Facility, Interest Rate at Period End | Rate					3.57%
Contractual Quarterly Payments							$ 2,100
Leverage ratio					1.89
Letters of Credit Outstanding, Amount					$ 4,400	4,000
Maximum [Member]
Debt Instrument [Line Items]
Leverage ratio					4.00
Leverage Ratio in Latest Year of Debt Term					3.25
$825 Million Term B Loan Facility and $150 Million Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Face amount of term loan							975,000
$150 Million Revolving Credit Facility, Due June 2020 [Member]
Debt Instrument [Line Items]
Secured Debt					$ 0	0
Face amount of term loan							150,000
$825 Million Term B Loan Facility, due June 2022 [Member]
Debt Instrument [Line Items]
Secured Debt					588,000	$ 656,000
Face amount of term loan							$ 825,000
$200 Million Revolving Credit Facility, Due February 2022 [Member]
Debt Instrument [Line Items]
Face amount of term loan			$ 200,000
Term Loan Facility | $825 Million Term B Loan Facility, due June 2022 [Member]
Debt Instrument [Line Items]
Basis spread on variable rate borrowings | Rate		0.25%	0.50%	0.25%
Term Loan Facility | $825 Million Term B Loan Facility, due June 2022 [Member] | Eurodollar [Member] | Maximum [Member]
Debt Instrument [Line Items]
Basis spread on variable rate borrowings | Rate		2.00%
Term Loan Facility | $200 Million Revolving Credit Facility, Due February 2022 [Member]
Debt Instrument [Line Items]
Basis spread on variable rate borrowings | Rate	0.50%
Term Loan Facility | $200 Million Revolving Credit Facility, Due February 2022 [Member] | Maximum [Member]
Debt Instrument [Line Items]
Basis spread on variable rate borrowings | Rate	1.25%
Revolving credit facility, unused portion, commitment fee percentage | Rate	0.35%
Term Loan Facility | $200 Million Revolving Credit Facility, Due February 2022 [Member] | Minimum [Member]
Debt Instrument [Line Items]
Basis spread on variable rate borrowings | Rate	0.25%
Revolving credit facility, unused portion, commitment fee percentage | Rate	0.20%
LineofCreditFacilityUnusedCapacityReductioninCommitmentFee | Rate	0.05%
Term Loan Facility | $200 Million Revolving Credit Facility, Due February 2022 [Member] | Eurodollar [Member] | Maximum [Member]
Debt Instrument [Line Items]
Basis spread on variable rate borrowings | Rate	2.25%
Term Loan Facility | $200 Million Revolving Credit Facility, Due February 2022 [Member] | Eurodollar [Member] | Minimum [Member]
Debt Instrument [Line Items]
Basis spread on variable rate borrowings | Rate	1.25%
Revolving Credit Facility
Debt Instrument [Line Items]
Line of Credit Facility, Remaining Borrowing Capacity					195,600
Interest Expense [Member]
Debt Instrument [Line Items]
Creditfacilityamendmentcosts					$ 2,700

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