Long-term Debt (Details) - USD ($)		12 Months Ended
	May 25, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2017
Line of Credit Facility [Line Items]
Repayments of credit facility	$ 382,000,000
Long-term debt			$ 383,137,000
Interest expense, debt		$ 14,500,000	15,000,000	$ 15,100,000
Interest costs capitalized		3,400,000	400,000	$ 0
Long-term Debt, by Current and Noncurrent [Abstract]
Term loan			383,137,000
Less current maturities		(4,000,000)	(3,960,000)		$ (4,000,000)
Total long-term debt		$ 389,914,000	379,177,000		$ 389,914,000
Amended Facility
Line of Credit Facility [Line Items]
Debt covenant, reduction of basis spread		0.25%
Covenant for marginal rates, secured leverage ratio		1.00
Secured leverage ratio		4.00
Debt issuance costs	4,400,000
Long-term debt		$ 393,914,000	$ 383,100,000
Effective interest rate		3.72%	3.79%
Additional borrowings	0		$ 0
Long-term Debt, by Current and Noncurrent [Abstract]
Term loan		$ 393,914,000	383,100,000
Amended Facility | Term Facility [Member]
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity	400,000,000.000000
Periodic principal payment	1,000,000
Periodic payment, balloon payment to be paid	373,000,000
Amended Facility | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity	120,000,000.000000
Debt fee amount	300,000
Amended Facility | Letter of Credit [Member]
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity	$ 10,000,000
Amended Facility | Variable rate option 1 | Federal Funds Effective Swap Rate [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.50%
Amended Facility | Variable rate option 1 | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.00%
Amended Facility | Variable rate option 1 | Base Rate [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.00%
Amended Facility | Variable rate option 1 | London Interbank Offer Rate, One Month (LIBOR) [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.00%
Amended Facility | Variable rate option 2 | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.00%
Amended Facility | Variable rate option 2 | Base Rate [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.00%
Amended Facility | Level 2
Line of Credit Facility [Line Items]
Long-term debt, fair value		$ 395,400,000	$ 386,500,000