Fair Market Value of Investments with Unrealized Losses Not Deemed to be Other-Than Temporarily Impaired (Detail) $ in Thousands	Sep. 29, 2018 USD ($)
Debt Securities, Available-for-sale [Line Items]
Unrealized Loss Position, Less than 12 Months, Fair Value	$ 6,440
Unrealized Loss Position, Less than 12 Months, Gross Unrealized Losses	22
Unrealized Loss Position, Greater than 12 Months, Fair Value	4,537
Unrealized Loss Position, Greater than 12 Months, Gross Unrealized Losses	19
Corporate bonds and medium-term notes
Debt Securities, Available-for-sale [Line Items]
Unrealized Loss Position, Less than 12 Months, Fair Value	2,925
Unrealized Loss Position, Less than 12 Months, Gross Unrealized Losses	10
Unrealized Loss Position, Greater than 12 Months, Fair Value	1,950
Unrealized Loss Position, Greater than 12 Months, Gross Unrealized Losses	8
Municipal bonds
Debt Securities, Available-for-sale [Line Items]
Unrealized Loss Position, Less than 12 Months, Fair Value	497
Unrealized Loss Position, Less than 12 Months, Gross Unrealized Losses	2
U.S. treasury and agency securities
Debt Securities, Available-for-sale [Line Items]
Unrealized Loss Position, Less than 12 Months, Fair Value	3,018
Unrealized Loss Position, Less than 12 Months, Gross Unrealized Losses	10
Unrealized Loss Position, Greater than 12 Months, Fair Value	2,587
Unrealized Loss Position, Greater than 12 Months, Gross Unrealized Losses	$ 11