Fair value measurement - Financial Instruments Measured at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 28, 2014
Assets:
Deferred compensation investments	$ 77,199	$ 65,950
Available for sale investment	28,090
Total Assets	105,289	65,950
Liabilities:
Contingent consideration payable		8,936
Total Liabilities		8,936
Level 1
Assets:
Deferred compensation investments	77,199	65,950
Available for sale investment	28,090
Total Assets	105,289	65,950
Liabilities:
Contingent consideration payable		0
Total Liabilities		0
Level 2
Assets:
Deferred compensation investments	0	0
Available for sale investment	0
Total Assets	0	0
Liabilities:
Contingent consideration payable		0
Total Liabilities		0
Level 3
Assets:
Deferred compensation investments	0	0
Available for sale investment	0
Total Assets	$ 0	0
Liabilities:
Contingent consideration payable		8,936
Total Liabilities		$ 8,936