Bank Note Payable and Term Note Payable (Details) $ in Thousands			6 Months Ended
	Aug. 26, 2013	Sep. 27, 2012 USD ($)	Jun. 30, 2018 USD ($) period	Dec. 31, 2017 USD ($)	Oct. 18, 2017 USD ($)
Debt Instrument [Line Items]
Borrowings outstanding			$ 98,000	$ 78,000
Senior Notes
Debt Instrument [Line Items]
Principal amount of loan			$ 200,000
Fixed charge coverage ratio			1.50
Series A Notes
Debt Instrument [Line Items]
Principal amount of loan			$ 116,000
Interest rate (as a percent)			3.99%
Series B Notes
Debt Instrument [Line Items]
Principal amount of loan			$ 84,000
Interest rate (as a percent)			4.26%
Maximum | Senior Notes
Debt Instrument [Line Items]
Unsecured leverage ratio			60.00%
Unsecured leverage ratio for significant acquisition			65.00%
BAML Revolver
Debt Instrument [Line Items]
Weighted average interest rate (as a percent)			2.96%
Effective interest rate (as a percent)			3.24%	2.63%
Total available			$ 600,000
Number of periods of extension | period			2
Length of extension period			6 months
Additional borrowing capacity allowed by exercising an accordion feature			$ 500,000
Borrowings outstanding			$ 98,000	$ 78,000
Facility fee at period end (as a percent)			0.25%
BAML Revolver | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate at period end (as a percent)			1.20%
BAML Revolver | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate at period end (as a percent)			0.20%
BAML Term Loan
Debt Instrument [Line Items]
Principal amount of loan			$ 400,000
Effective interest rate (as a percent)			2.47%
Additional borrowing capacity allowed by exercising an accordion feature			$ 500,000
Amount drawn down		$ 400,000
BAML Term Loan | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate at period end (as a percent)			1.35%
Fixed rate (as a percent)		0.75%	1.12%
Term pursuant to interest rate swap agreement		5 years
BAML Term Loan | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate at period end (as a percent)			0.35%
JPM Term Loan
Debt Instrument [Line Items]
Principal amount of loan					$ 150,000
Term of the borrowing			2 years
Interest rate during period (as a percent)			3.48%
Weighted average interest rate (as a percent)			3.16%	2.45%
JPM Term Loan | Eurodollar Rate
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)			1.35%
JPM Term Loan | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate at period end (as a percent)			35.00%
BMO Term Loan
Debt Instrument [Line Items]
Principal amount of loan			$ 220,000
Additional loans allowed by exercising an accordion feature			$ 50,000
Effective interest rate (as a percent)			3.97%
BMO Term Loan | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate at period end (as a percent)			1.65%
Fixed rate (as a percent)			2.32%
Term pursuant to interest rate swap agreement	7 years
BMO Term Loan | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate at period end (as a percent)			0.65%