Debt - Long-Term Debt - (Details) - USD ($)		3 Months Ended	9 Months Ended		12 Months Ended
	Aug. 10, 2015	Sep. 27, 2015	Sep. 27, 2015	Sep. 28, 2014	Dec. 31, 2014
Long-term debt
Revolving credit facility		$ 90,500,000	$ 90,500,000		$ 75,000,000
Revolving credit facility - terms
Borrowings repaid on previous credit facility			943,300,000	$ 757,700,000
Amortization expenses		61,000	165,000
Revolving credit facility due 2017 | Line of Credit
Long-term debt
Revolving credit facility					$ 75,000,000
Weighted-average interest rate					1.50%
Amount available					$ 122,535,000
Total credit facility					200,000,000
Standby letters of credit					$ 2,465,000
Commitment fee percentage per annum					0.25%
Revolving credit facility due 2020 | Line of Credit
Long-term debt
Revolving credit facility		$ 90,500,000	$ 90,500,000
Weighted-average interest rate		1.50%	1.50%
Amount available		$ 107,185,000	$ 107,185,000
Total credit facility	$ 200,000,000	200,000,000	200,000,000
Standby letters of credit		$ 2,315,000	$ 2,315,000
Commitment fee percentage per annum			0.30%
Revolving credit facility - terms
Term of credit agreement (in years)	5 years
Increase in maximum borrowing capacity subject to approval	$ 100,000,000
Revolving credit facility due 2020 | Line of Credit | Minimum
Long-term debt
Commitment fee percentage per annum	0.20%
Revolving credit facility due 2020 | Line of Credit | Maximum
Long-term debt
Commitment fee percentage per annum	0.40%
Swing line sublimit | Line of Credit
Long-term debt
Total credit facility	$ 15,000,000
Letter of credit sublimit | Line of Credit
Long-term debt
Total credit facility	$ 10,000,000