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Consolidated Statements of Stockholders' Equity (Parenthetical) - USD ($)
$ in Thousands
12 Months Ended
Dec. 30, 2017
Dec. 31, 2016
Dec. 26, 2015
Statement of Stockholders' Equity [Abstract]      
Adjustment related to unrealized gains (losses) on available-for-sale securities income tax effects $ 493 $ 1,094 $ 115