Fair Value Measurements and Disclosures - Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 26, 2015	Dec. 27, 2014
Assets:
Total marketable securities	$ 44,931	$ 49,286
Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	5,158	610
Total marketable securities	44,931	49,286
Total	50,089	49,896
Liabilities:
Contingent consideration payable	1,490	2,397
Money market funds [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	590	610
Commercial paper and corporate debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	4,568	0
U.S. Treasury, U.S. Government and U.S. Government agency debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	24,565	23,034
Commercial paper, municipal securities and corporate debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	20,366	26,252
Cash [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	33,000	34,100
Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	590	610
Total marketable securities	4,401	2,497
Total	4,991	3,107
Liabilities:
Contingent consideration payable	0	0
Level 1 [Member] | Money market funds [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	590	610
Level 1 [Member] | Commercial paper and corporate debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	0	0
Level 1 [Member] | U.S. Treasury, U.S. Government and U.S. Government agency debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	4,401	2,497
Level 1 [Member] | Commercial paper, municipal securities and corporate debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	0	0
Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	4,568	0
Total marketable securities	40,530	46,789
Total	45,098	46,789
Liabilities:
Contingent consideration payable	0	0
Level 2 [Member] | Money market funds [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	0	0
Level 2 [Member] | Commercial paper and corporate debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	4,568	0
Level 2 [Member] | U.S. Treasury, U.S. Government and U.S. Government agency debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	20,164	20,537
Level 2 [Member] | Commercial paper, municipal securities and corporate debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	20,366	26,252
Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	0	0
Total marketable securities	0	0
Total	0	0
Liabilities:
Contingent consideration payable	1,490	2,397
Level 3 [Member] | Money market funds [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	0	0
Level 3 [Member] | Commercial paper and corporate debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total cash equivalents	0	0
Level 3 [Member] | U.S. Treasury, U.S. Government and U.S. Government agency debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	0	0
Level 3 [Member] | Commercial paper, municipal securities and corporate debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Total marketable securities	$ 0	$ 0