Cash, Cash Equivalents And Short Term Investments (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Jan. 01, 2016
Fair Value Measurements [Line Items]
Amortized Cost	$ 150,419	$ 171,699
Unrealized Gains	14	1
Unrealized Losses	(15)	(107)
Estimated Fair Value	150,418	171,593
U.S. agency securities
Fair Value Measurements [Line Items]
Amortized Cost	51,994	41,946
Unrealized Gains	14	1
Unrealized Losses	(15)	(106)
Estimated Fair Value	51,993	41,841
Cash
Fair Value Measurements [Line Items]
Amortized Cost	69,524	115,221
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated Fair Value	69,524	115,221
Money market securities
Fair Value Measurements [Line Items]
Amortized Cost	28,901	10,530
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated Fair Value	28,901	10,530
Total cash equivalents
Fair Value Measurements [Line Items]
Amortized Cost	28,901	10,530
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated Fair Value	28,901	10,530
Total cash and cash equivalents
Fair Value Measurements [Line Items]
Amortized Cost	98,425	125,751
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated Fair Value	98,425	125,751
State and municipal bonds
Fair Value Measurements [Line Items]
Amortized Cost		4,002
Unrealized Gains		0
Unrealized Losses		(1)
Estimated Fair Value		4,001
Total short-term investments
Fair Value Measurements [Line Items]
Amortized Cost	51,994	45,948
Unrealized Gains	14	1
Unrealized Losses	(15)	(107)
Estimated Fair Value	$ 51,993	$ 45,842