Investments - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 27, 2014	Dec. 28, 2013
Schedule of Available-for-sale Securities [Line Items]
Investments maximum maturity period	5 years	5 years
Unrealized gains, net of unrealized losses, on the investments in the bond portfolio	$ 163,000	$ 378,000
Guarantee Payment Of Insurance Claims
Schedule of Available-for-sale Securities [Line Items]
Letters of credit outstanding	63,761,000
Current Investments
Schedule of Available-for-sale Securities [Line Items]
Investments providing collateral for letters of credit to guarantee insurance claims	37,007,000
Non-Current Investments
Schedule of Available-for-sale Securities [Line Items]
Investments providing collateral for letters of credit to guarantee insurance claims	33,839,000
Total non-current investments	$ 66,462,000