MARKETABLE SECURITIES - Available-for-sale Securities (Details) (USD $) In Thousands, unless otherwise specified	Sep. 26, 2014		Dec. 27, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,750		$ 20,750	[1]
Fair Value	1,746		20,650
Certificates of deposit (1)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,750	[1]	10,000	[1]
Fair Value	1,746	[1]	9,900	[1]
Variable-rate demand notes
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	0		5,750
Fair Value	0		5,750
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	0		5,000
Fair Value	$ 0		$ 5,000

[1] As of September 26, 2014, all our certificate of deposits were due within one year.